src/HOL/Multivariate_Analysis/Topology_Euclidean_Space.thy

clarified Token.range_of in accordance to Symbol_Pos.range;
eliminated redundant Position.set_range, which is already included in Position.range;

(*  title:      HOL/Library/Topology_Euclidian_Space.thy
    Author:     Amine Chaieb, University of Cambridge
    Author:     Robert Himmelmann, TU Muenchen
    Author:     Brian Huffman, Portland State University
*)

header {* Elementary topology in Euclidean space. *}

theory Topology_Euclidean_Space
imports
  Complex_Main
  "~~/src/HOL/Library/Countable_Set"
  "~~/src/HOL/Library/FuncSet"
  Linear_Algebra
  Norm_Arith
begin

lemma dist_0_norm:
  fixes x :: "'a::real_normed_vector"
  shows "dist 0 x = norm x"
unfolding dist_norm by simp

lemma dist_double: "dist x y < d / 2 \<Longrightarrow> dist x z < d / 2 \<Longrightarrow> dist y z < d"
  using dist_triangle[of y z x] by (simp add: dist_commute)

(* LEGACY *)
lemma lim_subseq: "subseq r \<Longrightarrow> s ----> l \<Longrightarrow> (s \<circ> r) ----> l"
  by (rule LIMSEQ_subseq_LIMSEQ)

lemma countable_PiE:
  "finite I \<Longrightarrow> (\<And>i. i \<in> I \<Longrightarrow> countable (F i)) \<Longrightarrow> countable (PiE I F)"
  by (induct I arbitrary: F rule: finite_induct) (auto simp: PiE_insert_eq)

lemma Lim_within_open:
  fixes f :: "'a::topological_space \<Rightarrow> 'b::topological_space"
  shows "a \<in> S \<Longrightarrow> open S \<Longrightarrow> (f ---> l)(at a within S) \<longleftrightarrow> (f ---> l)(at a)"
  by (fact tendsto_within_open)

lemma continuous_on_union:
  "closed s \<Longrightarrow> closed t \<Longrightarrow> continuous_on s f \<Longrightarrow> continuous_on t f \<Longrightarrow> continuous_on (s \<union> t) f"
  by (fact continuous_on_closed_Un)

lemma continuous_on_cases:
  "closed s \<Longrightarrow> closed t \<Longrightarrow> continuous_on s f \<Longrightarrow> continuous_on t g \<Longrightarrow>
    \<forall>x. (x\<in>s \<and> \<not> P x) \<or> (x \<in> t \<and> P x) \<longrightarrow> f x = g x \<Longrightarrow>
    continuous_on (s \<union> t) (\<lambda>x. if P x then f x else g x)"
  by (rule continuous_on_If) auto


subsection {* Topological Basis *}

context topological_space
begin

definition "topological_basis B \<longleftrightarrow>
  (\<forall>b\<in>B. open b) \<and> (\<forall>x. open x \<longrightarrow> (\<exists>B'. B' \<subseteq> B \<and> \<Union>B' = x))"

lemma topological_basis:
  "topological_basis B \<longleftrightarrow> (\<forall>x. open x \<longleftrightarrow> (\<exists>B'. B' \<subseteq> B \<and> \<Union>B' = x))"
  unfolding topological_basis_def
  apply safe
     apply fastforce
    apply fastforce
   apply (erule_tac x="x" in allE)
   apply simp
   apply (rule_tac x="{x}" in exI)
  apply auto
  done

lemma topological_basis_iff:
  assumes "\<And>B'. B' \<in> B \<Longrightarrow> open B'"
  shows "topological_basis B \<longleftrightarrow> (\<forall>O'. open O' \<longrightarrow> (\<forall>x\<in>O'. \<exists>B'\<in>B. x \<in> B' \<and> B' \<subseteq> O'))"
    (is "_ \<longleftrightarrow> ?rhs")
proof safe
  fix O' and x::'a
  assume H: "topological_basis B" "open O'" "x \<in> O'"
  then have "(\<exists>B'\<subseteq>B. \<Union>B' = O')" by (simp add: topological_basis_def)
  then obtain B' where "B' \<subseteq> B" "O' = \<Union>B'" by auto
  then show "\<exists>B'\<in>B. x \<in> B' \<and> B' \<subseteq> O'" using H by auto
next
  assume H: ?rhs
  show "topological_basis B"
    using assms unfolding topological_basis_def
  proof safe
    fix O' :: "'a set"
    assume "open O'"
    with H obtain f where "\<forall>x\<in>O'. f x \<in> B \<and> x \<in> f x \<and> f x \<subseteq> O'"
      by (force intro: bchoice simp: Bex_def)
    then show "\<exists>B'\<subseteq>B. \<Union>B' = O'"
      by (auto intro: exI[where x="{f x |x. x \<in> O'}"])
  qed
qed

lemma topological_basisI:
  assumes "\<And>B'. B' \<in> B \<Longrightarrow> open B'"
    and "\<And>O' x. open O' \<Longrightarrow> x \<in> O' \<Longrightarrow> \<exists>B'\<in>B. x \<in> B' \<and> B' \<subseteq> O'"
  shows "topological_basis B"
  using assms by (subst topological_basis_iff) auto

lemma topological_basisE:
  fixes O'
  assumes "topological_basis B"
    and "open O'"
    and "x \<in> O'"
  obtains B' where "B' \<in> B" "x \<in> B'" "B' \<subseteq> O'"
proof atomize_elim
  from assms have "\<And>B'. B'\<in>B \<Longrightarrow> open B'"
    by (simp add: topological_basis_def)
  with topological_basis_iff assms
  show  "\<exists>B'. B' \<in> B \<and> x \<in> B' \<and> B' \<subseteq> O'"
    using assms by (simp add: Bex_def)
qed

lemma topological_basis_open:
  assumes "topological_basis B"
    and "X \<in> B"
  shows "open X"
  using assms by (simp add: topological_basis_def)

lemma topological_basis_imp_subbasis:
  assumes B: "topological_basis B"
  shows "open = generate_topology B"
proof (intro ext iffI)
  fix S :: "'a set"
  assume "open S"
  with B obtain B' where "B' \<subseteq> B" "S = \<Union>B'"
    unfolding topological_basis_def by blast
  then show "generate_topology B S"
    by (auto intro: generate_topology.intros dest: topological_basis_open)
next
  fix S :: "'a set"
  assume "generate_topology B S"
  then show "open S"
    by induct (auto dest: topological_basis_open[OF B])
qed

lemma basis_dense:
  fixes B :: "'a set set"
    and f :: "'a set \<Rightarrow> 'a"
  assumes "topological_basis B"
    and choosefrom_basis: "\<And>B'. B' \<noteq> {} \<Longrightarrow> f B' \<in> B'"
  shows "\<forall>X. open X \<longrightarrow> X \<noteq> {} \<longrightarrow> (\<exists>B' \<in> B. f B' \<in> X)"
proof (intro allI impI)
  fix X :: "'a set"
  assume "open X" and "X \<noteq> {}"
  from topological_basisE[OF `topological_basis B` `open X` choosefrom_basis[OF `X \<noteq> {}`]]
  obtain B' where "B' \<in> B" "f X \<in> B'" "B' \<subseteq> X" .
  then show "\<exists>B'\<in>B. f B' \<in> X"
    by (auto intro!: choosefrom_basis)
qed

end

lemma topological_basis_prod:
  assumes A: "topological_basis A"
    and B: "topological_basis B"
  shows "topological_basis ((\<lambda>(a, b). a \<times> b) ` (A \<times> B))"
  unfolding topological_basis_def
proof (safe, simp_all del: ex_simps add: subset_image_iff ex_simps(1)[symmetric])
  fix S :: "('a \<times> 'b) set"
  assume "open S"
  then show "\<exists>X\<subseteq>A \<times> B. (\<Union>(a,b)\<in>X. a \<times> b) = S"
  proof (safe intro!: exI[of _ "{x\<in>A \<times> B. fst x \<times> snd x \<subseteq> S}"])
    fix x y
    assume "(x, y) \<in> S"
    from open_prod_elim[OF `open S` this]
    obtain a b where a: "open a""x \<in> a" and b: "open b" "y \<in> b" and "a \<times> b \<subseteq> S"
      by (metis mem_Sigma_iff)
    moreover
    from A a obtain A0 where "A0 \<in> A" "x \<in> A0" "A0 \<subseteq> a"
      by (rule topological_basisE)
    moreover
    from B b obtain B0 where "B0 \<in> B" "y \<in> B0" "B0 \<subseteq> b"
      by (rule topological_basisE)
    ultimately show "(x, y) \<in> (\<Union>(a, b)\<in>{X \<in> A \<times> B. fst X \<times> snd X \<subseteq> S}. a \<times> b)"
      by (intro UN_I[of "(A0, B0)"]) auto
  qed auto
qed (metis A B topological_basis_open open_Times)


subsection {* Countable Basis *}

locale countable_basis =
  fixes B :: "'a::topological_space set set"
  assumes is_basis: "topological_basis B"
    and countable_basis: "countable B"
begin

lemma open_countable_basis_ex:
  assumes "open X"
  shows "\<exists>B' \<subseteq> B. X = Union B'"
  using assms countable_basis is_basis
  unfolding topological_basis_def by blast

lemma open_countable_basisE:
  assumes "open X"
  obtains B' where "B' \<subseteq> B" "X = Union B'"
  using assms open_countable_basis_ex
  by (atomize_elim) simp

lemma countable_dense_exists:
  "\<exists>D::'a set. countable D \<and> (\<forall>X. open X \<longrightarrow> X \<noteq> {} \<longrightarrow> (\<exists>d \<in> D. d \<in> X))"
proof -
  let ?f = "(\<lambda>B'. SOME x. x \<in> B')"
  have "countable (?f ` B)" using countable_basis by simp
  with basis_dense[OF is_basis, of ?f] show ?thesis
    by (intro exI[where x="?f ` B"]) (metis (mono_tags) all_not_in_conv imageI someI)
qed

lemma countable_dense_setE:
  obtains D :: "'a set"
  where "countable D" "\<And>X. open X \<Longrightarrow> X \<noteq> {} \<Longrightarrow> \<exists>d \<in> D. d \<in> X"
  using countable_dense_exists by blast

end

lemma (in first_countable_topology) first_countable_basisE:
  obtains A where "countable A" "\<And>a. a \<in> A \<Longrightarrow> x \<in> a" "\<And>a. a \<in> A \<Longrightarrow> open a"
    "\<And>S. open S \<Longrightarrow> x \<in> S \<Longrightarrow> (\<exists>a\<in>A. a \<subseteq> S)"
  using first_countable_basis[of x]
  apply atomize_elim
  apply (elim exE)
  apply (rule_tac x="range A" in exI)
  apply auto
  done

lemma (in first_countable_topology) first_countable_basis_Int_stableE:
  obtains A where "countable A" "\<And>a. a \<in> A \<Longrightarrow> x \<in> a" "\<And>a. a \<in> A \<Longrightarrow> open a"
    "\<And>S. open S \<Longrightarrow> x \<in> S \<Longrightarrow> (\<exists>a\<in>A. a \<subseteq> S)"
    "\<And>a b. a \<in> A \<Longrightarrow> b \<in> A \<Longrightarrow> a \<inter> b \<in> A"
proof atomize_elim
  obtain A' where A':
    "countable A'"
    "\<And>a. a \<in> A' \<Longrightarrow> x \<in> a"
    "\<And>a. a \<in> A' \<Longrightarrow> open a"
    "\<And>S. open S \<Longrightarrow> x \<in> S \<Longrightarrow> \<exists>a\<in>A'. a \<subseteq> S"
    by (rule first_countable_basisE) blast
  def A \<equiv> "(\<lambda>N. \<Inter>((\<lambda>n. from_nat_into A' n) ` N)) ` (Collect finite::nat set set)"
  then show "\<exists>A. countable A \<and> (\<forall>a. a \<in> A \<longrightarrow> x \<in> a) \<and> (\<forall>a. a \<in> A \<longrightarrow> open a) \<and>
        (\<forall>S. open S \<longrightarrow> x \<in> S \<longrightarrow> (\<exists>a\<in>A. a \<subseteq> S)) \<and> (\<forall>a b. a \<in> A \<longrightarrow> b \<in> A \<longrightarrow> a \<inter> b \<in> A)"
  proof (safe intro!: exI[where x=A])
    show "countable A"
      unfolding A_def by (intro countable_image countable_Collect_finite)
    fix a
    assume "a \<in> A"
    then show "x \<in> a" "open a"
      using A'(4)[OF open_UNIV] by (auto simp: A_def intro: A' from_nat_into)
  next
    let ?int = "\<lambda>N. \<Inter>(from_nat_into A' ` N)"
    fix a b
    assume "a \<in> A" "b \<in> A"
    then obtain N M where "a = ?int N" "b = ?int M" "finite (N \<union> M)"
      by (auto simp: A_def)
    then show "a \<inter> b \<in> A"
      by (auto simp: A_def intro!: image_eqI[where x="N \<union> M"])
  next
    fix S
    assume "open S" "x \<in> S"
    then obtain a where a: "a\<in>A'" "a \<subseteq> S" using A' by blast
    then show "\<exists>a\<in>A. a \<subseteq> S" using a A'
      by (intro bexI[where x=a]) (auto simp: A_def intro: image_eqI[where x="{to_nat_on A' a}"])
  qed
qed

lemma (in topological_space) first_countableI:
  assumes "countable A"
    and 1: "\<And>a. a \<in> A \<Longrightarrow> x \<in> a" "\<And>a. a \<in> A \<Longrightarrow> open a"
    and 2: "\<And>S. open S \<Longrightarrow> x \<in> S \<Longrightarrow> \<exists>a\<in>A. a \<subseteq> S"
  shows "\<exists>A::nat \<Rightarrow> 'a set. (\<forall>i. x \<in> A i \<and> open (A i)) \<and> (\<forall>S. open S \<and> x \<in> S \<longrightarrow> (\<exists>i. A i \<subseteq> S))"
proof (safe intro!: exI[of _ "from_nat_into A"])
  fix i
  have "A \<noteq> {}" using 2[of UNIV] by auto
  show "x \<in> from_nat_into A i" "open (from_nat_into A i)"
    using range_from_nat_into_subset[OF `A \<noteq> {}`] 1 by auto
next
  fix S
  assume "open S" "x\<in>S" from 2[OF this]
  show "\<exists>i. from_nat_into A i \<subseteq> S"
    using subset_range_from_nat_into[OF `countable A`] by auto
qed

instance prod :: (first_countable_topology, first_countable_topology) first_countable_topology
proof
  fix x :: "'a \<times> 'b"
  obtain A where A:
      "countable A"
      "\<And>a. a \<in> A \<Longrightarrow> fst x \<in> a"
      "\<And>a. a \<in> A \<Longrightarrow> open a"
      "\<And>S. open S \<Longrightarrow> fst x \<in> S \<Longrightarrow> \<exists>a\<in>A. a \<subseteq> S"
    by (rule first_countable_basisE[of "fst x"]) blast
  obtain B where B:
      "countable B"
      "\<And>a. a \<in> B \<Longrightarrow> snd x \<in> a"
      "\<And>a. a \<in> B \<Longrightarrow> open a"
      "\<And>S. open S \<Longrightarrow> snd x \<in> S \<Longrightarrow> \<exists>a\<in>B. a \<subseteq> S"
    by (rule first_countable_basisE[of "snd x"]) blast
  show "\<exists>A::nat \<Rightarrow> ('a \<times> 'b) set.
    (\<forall>i. x \<in> A i \<and> open (A i)) \<and> (\<forall>S. open S \<and> x \<in> S \<longrightarrow> (\<exists>i. A i \<subseteq> S))"
  proof (rule first_countableI[of "(\<lambda>(a, b). a \<times> b) ` (A \<times> B)"], safe)
    fix a b
    assume x: "a \<in> A" "b \<in> B"
    with A(2, 3)[of a] B(2, 3)[of b] show "x \<in> a \<times> b" and "open (a \<times> b)"
      unfolding mem_Times_iff
      by (auto intro: open_Times)
  next
    fix S
    assume "open S" "x \<in> S"
    then obtain a' b' where a'b': "open a'" "open b'" "x \<in> a' \<times> b'" "a' \<times> b' \<subseteq> S"
      by (rule open_prod_elim)
    moreover
    from a'b' A(4)[of a'] B(4)[of b']
    obtain a b where "a \<in> A" "a \<subseteq> a'" "b \<in> B" "b \<subseteq> b'"
      by auto
    ultimately
    show "\<exists>a\<in>(\<lambda>(a, b). a \<times> b) ` (A \<times> B). a \<subseteq> S"
      by (auto intro!: bexI[of _ "a \<times> b"] bexI[of _ a] bexI[of _ b])
  qed (simp add: A B)
qed

class second_countable_topology = topological_space +
  assumes ex_countable_subbasis:
    "\<exists>B::'a::topological_space set set. countable B \<and> open = generate_topology B"
begin

lemma ex_countable_basis: "\<exists>B::'a set set. countable B \<and> topological_basis B"
proof -
  from ex_countable_subbasis obtain B where B: "countable B" "open = generate_topology B"
    by blast
  let ?B = "Inter ` {b. finite b \<and> b \<subseteq> B }"

  show ?thesis
  proof (intro exI conjI)
    show "countable ?B"
      by (intro countable_image countable_Collect_finite_subset B)
    {
      fix S
      assume "open S"
      then have "\<exists>B'\<subseteq>{b. finite b \<and> b \<subseteq> B}. (\<Union>b\<in>B'. \<Inter>b) = S"
        unfolding B
      proof induct
        case UNIV
        show ?case by (intro exI[of _ "{{}}"]) simp
      next
        case (Int a b)
        then obtain x y where x: "a = UNION x Inter" "\<And>i. i \<in> x \<Longrightarrow> finite i \<and> i \<subseteq> B"
          and y: "b = UNION y Inter" "\<And>i. i \<in> y \<Longrightarrow> finite i \<and> i \<subseteq> B"
          by blast
        show ?case
          unfolding x y Int_UN_distrib2
          by (intro exI[of _ "{i \<union> j| i j.  i \<in> x \<and> j \<in> y}"]) (auto dest: x(2) y(2))
      next
        case (UN K)
        then have "\<forall>k\<in>K. \<exists>B'\<subseteq>{b. finite b \<and> b \<subseteq> B}. UNION B' Inter = k" by auto
        then obtain k where
            "\<forall>ka\<in>K. k ka \<subseteq> {b. finite b \<and> b \<subseteq> B} \<and> UNION (k ka) Inter = ka"
          unfolding bchoice_iff ..
        then show "\<exists>B'\<subseteq>{b. finite b \<and> b \<subseteq> B}. UNION B' Inter = \<Union>K"
          by (intro exI[of _ "UNION K k"]) auto
      next
        case (Basis S)
        then show ?case
          by (intro exI[of _ "{{S}}"]) auto
      qed
      then have "(\<exists>B'\<subseteq>Inter ` {b. finite b \<and> b \<subseteq> B}. \<Union>B' = S)"
        unfolding subset_image_iff by blast }
    then show "topological_basis ?B"
      unfolding topological_space_class.topological_basis_def
      by (safe intro!: topological_space_class.open_Inter)
         (simp_all add: B generate_topology.Basis subset_eq)
  qed
qed

end

sublocale second_countable_topology <
  countable_basis "SOME B. countable B \<and> topological_basis B"
  using someI_ex[OF ex_countable_basis]
  by unfold_locales safe

instance prod :: (second_countable_topology, second_countable_topology) second_countable_topology
proof
  obtain A :: "'a set set" where "countable A" "topological_basis A"
    using ex_countable_basis by auto
  moreover
  obtain B :: "'b set set" where "countable B" "topological_basis B"
    using ex_countable_basis by auto
  ultimately show "\<exists>B::('a \<times> 'b) set set. countable B \<and> open = generate_topology B"
    by (auto intro!: exI[of _ "(\<lambda>(a, b). a \<times> b) ` (A \<times> B)"] topological_basis_prod
      topological_basis_imp_subbasis)
qed

instance second_countable_topology \<subseteq> first_countable_topology
proof
  fix x :: 'a
  def B \<equiv> "SOME B::'a set set. countable B \<and> topological_basis B"
  then have B: "countable B" "topological_basis B"
    using countable_basis is_basis
    by (auto simp: countable_basis is_basis)
  then show "\<exists>A::nat \<Rightarrow> 'a set.
    (\<forall>i. x \<in> A i \<and> open (A i)) \<and> (\<forall>S. open S \<and> x \<in> S \<longrightarrow> (\<exists>i. A i \<subseteq> S))"
    by (intro first_countableI[of "{b\<in>B. x \<in> b}"])
       (fastforce simp: topological_space_class.topological_basis_def)+
qed


subsection {* Polish spaces *}

text {* Textbooks define Polish spaces as completely metrizable.
  We assume the topology to be complete for a given metric. *}

class polish_space = complete_space + second_countable_topology

subsection {* General notion of a topology as a value *}

definition "istopology L \<longleftrightarrow>
  L {} \<and> (\<forall>S T. L S \<longrightarrow> L T \<longrightarrow> L (S \<inter> T)) \<and> (\<forall>K. Ball K L \<longrightarrow> L (\<Union> K))"

typedef 'a topology = "{L::('a set) \<Rightarrow> bool. istopology L}"
  morphisms "openin" "topology"
  unfolding istopology_def by blast

lemma istopology_open_in[intro]: "istopology(openin U)"
  using openin[of U] by blast

lemma topology_inverse': "istopology U \<Longrightarrow> openin (topology U) = U"
  using topology_inverse[unfolded mem_Collect_eq] .

lemma topology_inverse_iff: "istopology U \<longleftrightarrow> openin (topology U) = U"
  using topology_inverse[of U] istopology_open_in[of "topology U"] by auto

lemma topology_eq: "T1 = T2 \<longleftrightarrow> (\<forall>S. openin T1 S \<longleftrightarrow> openin T2 S)"
proof
  assume "T1 = T2"
  then show "\<forall>S. openin T1 S \<longleftrightarrow> openin T2 S" by simp
next
  assume H: "\<forall>S. openin T1 S \<longleftrightarrow> openin T2 S"
  then have "openin T1 = openin T2" by (simp add: fun_eq_iff)
  then have "topology (openin T1) = topology (openin T2)" by simp
  then show "T1 = T2" unfolding openin_inverse .
qed

text{* Infer the "universe" from union of all sets in the topology. *}

definition "topspace T = \<Union>{S. openin T S}"

subsubsection {* Main properties of open sets *}

lemma openin_clauses:
  fixes U :: "'a topology"
  shows
    "openin U {}"
    "\<And>S T. openin U S \<Longrightarrow> openin U T \<Longrightarrow> openin U (S\<inter>T)"
    "\<And>K. (\<forall>S \<in> K. openin U S) \<Longrightarrow> openin U (\<Union>K)"
  using openin[of U] unfolding istopology_def mem_Collect_eq by fast+

lemma openin_subset[intro]: "openin U S \<Longrightarrow> S \<subseteq> topspace U"
  unfolding topspace_def by blast

lemma openin_empty[simp]: "openin U {}"
  by (simp add: openin_clauses)

lemma openin_Int[intro]: "openin U S \<Longrightarrow> openin U T \<Longrightarrow> openin U (S \<inter> T)"
  using openin_clauses by simp

lemma openin_Union[intro]: "(\<forall>S \<in>K. openin U S) \<Longrightarrow> openin U (\<Union> K)"
  using openin_clauses by simp

lemma openin_Un[intro]: "openin U S \<Longrightarrow> openin U T \<Longrightarrow> openin U (S \<union> T)"
  using openin_Union[of "{S,T}" U] by auto

lemma openin_topspace[intro, simp]: "openin U (topspace U)"
  by (simp add: openin_Union topspace_def)

lemma openin_subopen: "openin U S \<longleftrightarrow> (\<forall>x \<in> S. \<exists>T. openin U T \<and> x \<in> T \<and> T \<subseteq> S)"
  (is "?lhs \<longleftrightarrow> ?rhs")
proof
  assume ?lhs
  then show ?rhs by auto
next
  assume H: ?rhs
  let ?t = "\<Union>{T. openin U T \<and> T \<subseteq> S}"
  have "openin U ?t" by (simp add: openin_Union)
  also have "?t = S" using H by auto
  finally show "openin U S" .
qed


subsubsection {* Closed sets *}

definition "closedin U S \<longleftrightarrow> S \<subseteq> topspace U \<and> openin U (topspace U - S)"

lemma closedin_subset: "closedin U S \<Longrightarrow> S \<subseteq> topspace U"
  by (metis closedin_def)

lemma closedin_empty[simp]: "closedin U {}"
  by (simp add: closedin_def)

lemma closedin_topspace[intro, simp]: "closedin U (topspace U)"
  by (simp add: closedin_def)

lemma closedin_Un[intro]: "closedin U S \<Longrightarrow> closedin U T \<Longrightarrow> closedin U (S \<union> T)"
  by (auto simp add: Diff_Un closedin_def)

lemma Diff_Inter[intro]: "A - \<Inter>S = \<Union> {A - s|s. s\<in>S}"
  by auto

lemma closedin_Inter[intro]:
  assumes Ke: "K \<noteq> {}"
    and Kc: "\<forall>S \<in>K. closedin U S"
  shows "closedin U (\<Inter> K)"
  using Ke Kc unfolding closedin_def Diff_Inter by auto

lemma closedin_Int[intro]: "closedin U S \<Longrightarrow> closedin U T \<Longrightarrow> closedin U (S \<inter> T)"
  using closedin_Inter[of "{S,T}" U] by auto

lemma Diff_Diff_Int: "A - (A - B) = A \<inter> B"
  by blast

lemma openin_closedin_eq: "openin U S \<longleftrightarrow> S \<subseteq> topspace U \<and> closedin U (topspace U - S)"
  apply (auto simp add: closedin_def Diff_Diff_Int inf_absorb2)
  apply (metis openin_subset subset_eq)
  done

lemma openin_closedin: "S \<subseteq> topspace U \<Longrightarrow> (openin U S \<longleftrightarrow> closedin U (topspace U - S))"
  by (simp add: openin_closedin_eq)

lemma openin_diff[intro]:
  assumes oS: "openin U S"
    and cT: "closedin U T"
  shows "openin U (S - T)"
proof -
  have "S - T = S \<inter> (topspace U - T)" using openin_subset[of U S]  oS cT
    by (auto simp add: topspace_def openin_subset)
  then show ?thesis using oS cT
    by (auto simp add: closedin_def)
qed

lemma closedin_diff[intro]:
  assumes oS: "closedin U S"
    and cT: "openin U T"
  shows "closedin U (S - T)"
proof -
  have "S - T = S \<inter> (topspace U - T)"
    using closedin_subset[of U S] oS cT by (auto simp add: topspace_def)
  then show ?thesis
    using oS cT by (auto simp add: openin_closedin_eq)
qed


subsubsection {* Subspace topology *}

definition "subtopology U V = topology (\<lambda>T. \<exists>S. T = S \<inter> V \<and> openin U S)"

lemma istopology_subtopology: "istopology (\<lambda>T. \<exists>S. T = S \<inter> V \<and> openin U S)"
  (is "istopology ?L")
proof -
  have "?L {}" by blast
  {
    fix A B
    assume A: "?L A" and B: "?L B"
    from A B obtain Sa and Sb where Sa: "openin U Sa" "A = Sa \<inter> V" and Sb: "openin U Sb" "B = Sb \<inter> V"
      by blast
    have "A \<inter> B = (Sa \<inter> Sb) \<inter> V" "openin U (Sa \<inter> Sb)"
      using Sa Sb by blast+
    then have "?L (A \<inter> B)" by blast
  }
  moreover
  {
    fix K
    assume K: "K \<subseteq> Collect ?L"
    have th0: "Collect ?L = (\<lambda>S. S \<inter> V) ` Collect (openin U)"
      apply (rule set_eqI)
      apply (simp add: Ball_def image_iff)
      apply metis
      done
    from K[unfolded th0 subset_image_iff]
    obtain Sk where Sk: "Sk \<subseteq> Collect (openin U)" "K = (\<lambda>S. S \<inter> V) ` Sk"
      by blast
    have "\<Union>K = (\<Union>Sk) \<inter> V"
      using Sk by auto
    moreover have "openin U (\<Union> Sk)"
      using Sk by (auto simp add: subset_eq)
    ultimately have "?L (\<Union>K)" by blast
  }
  ultimately show ?thesis
    unfolding subset_eq mem_Collect_eq istopology_def by blast
qed

lemma openin_subtopology: "openin (subtopology U V) S \<longleftrightarrow> (\<exists>T. openin U T \<and> S = T \<inter> V)"
  unfolding subtopology_def topology_inverse'[OF istopology_subtopology]
  by auto

lemma topspace_subtopology: "topspace (subtopology U V) = topspace U \<inter> V"
  by (auto simp add: topspace_def openin_subtopology)

lemma closedin_subtopology: "closedin (subtopology U V) S \<longleftrightarrow> (\<exists>T. closedin U T \<and> S = T \<inter> V)"
  unfolding closedin_def topspace_subtopology
  apply (simp add: openin_subtopology)
  apply (rule iffI)
  apply clarify
  apply (rule_tac x="topspace U - T" in exI)
  apply auto
  done

lemma openin_subtopology_refl: "openin (subtopology U V) V \<longleftrightarrow> V \<subseteq> topspace U"
  unfolding openin_subtopology
  apply (rule iffI, clarify)
  apply (frule openin_subset[of U])
  apply blast
  apply (rule exI[where x="topspace U"])
  apply auto
  done

lemma subtopology_superset:
  assumes UV: "topspace U \<subseteq> V"
  shows "subtopology U V = U"
proof -
  {
    fix S
    {
      fix T
      assume T: "openin U T" "S = T \<inter> V"
      from T openin_subset[OF T(1)] UV have eq: "S = T"
        by blast
      have "openin U S"
        unfolding eq using T by blast
    }
    moreover
    {
      assume S: "openin U S"
      then have "\<exists>T. openin U T \<and> S = T \<inter> V"
        using openin_subset[OF S] UV by auto
    }
    ultimately have "(\<exists>T. openin U T \<and> S = T \<inter> V) \<longleftrightarrow> openin U S"
      by blast
  }
  then show ?thesis
    unfolding topology_eq openin_subtopology by blast
qed

lemma subtopology_topspace[simp]: "subtopology U (topspace U) = U"
  by (simp add: subtopology_superset)

lemma subtopology_UNIV[simp]: "subtopology U UNIV = U"
  by (simp add: subtopology_superset)


subsubsection {* The standard Euclidean topology *}

definition euclidean :: "'a::topological_space topology"
  where "euclidean = topology open"

lemma open_openin: "open S \<longleftrightarrow> openin euclidean S"
  unfolding euclidean_def
  apply (rule cong[where x=S and y=S])
  apply (rule topology_inverse[symmetric])
  apply (auto simp add: istopology_def)
  done

lemma topspace_euclidean: "topspace euclidean = UNIV"
  apply (simp add: topspace_def)
  apply (rule set_eqI)
  apply (auto simp add: open_openin[symmetric])
  done

lemma topspace_euclidean_subtopology[simp]: "topspace (subtopology euclidean S) = S"
  by (simp add: topspace_euclidean topspace_subtopology)

lemma closed_closedin: "closed S \<longleftrightarrow> closedin euclidean S"
  by (simp add: closed_def closedin_def topspace_euclidean open_openin Compl_eq_Diff_UNIV)

lemma open_subopen: "open S \<longleftrightarrow> (\<forall>x\<in>S. \<exists>T. open T \<and> x \<in> T \<and> T \<subseteq> S)"
  by (simp add: open_openin openin_subopen[symmetric])

text {* Basic "localization" results are handy for connectedness. *}

lemma openin_open: "openin (subtopology euclidean U) S \<longleftrightarrow> (\<exists>T. open T \<and> (S = U \<inter> T))"
  by (auto simp add: openin_subtopology open_openin[symmetric])

lemma openin_open_Int[intro]: "open S \<Longrightarrow> openin (subtopology euclidean U) (U \<inter> S)"
  by (auto simp add: openin_open)

lemma open_openin_trans[trans]:
  "open S \<Longrightarrow> open T \<Longrightarrow> T \<subseteq> S \<Longrightarrow> openin (subtopology euclidean S) T"
  by (metis Int_absorb1  openin_open_Int)

lemma open_subset: "S \<subseteq> T \<Longrightarrow> open S \<Longrightarrow> openin (subtopology euclidean T) S"
  by (auto simp add: openin_open)

lemma closedin_closed: "closedin (subtopology euclidean U) S \<longleftrightarrow> (\<exists>T. closed T \<and> S = U \<inter> T)"
  by (simp add: closedin_subtopology closed_closedin Int_ac)

lemma closedin_closed_Int: "closed S \<Longrightarrow> closedin (subtopology euclidean U) (U \<inter> S)"
  by (metis closedin_closed)

lemma closed_closedin_trans:
  "closed S \<Longrightarrow> closed T \<Longrightarrow> T \<subseteq> S \<Longrightarrow> closedin (subtopology euclidean S) T"
  apply (subgoal_tac "S \<inter> T = T" )
  apply auto
  apply (frule closedin_closed_Int[of T S])
  apply simp
  done

lemma closed_subset: "S \<subseteq> T \<Longrightarrow> closed S \<Longrightarrow> closedin (subtopology euclidean T) S"
  by (auto simp add: closedin_closed)

lemma openin_euclidean_subtopology_iff:
  fixes S U :: "'a::metric_space set"
  shows "openin (subtopology euclidean U) S \<longleftrightarrow>
    S \<subseteq> U \<and> (\<forall>x\<in>S. \<exists>e>0. \<forall>x'\<in>U. dist x' x < e \<longrightarrow> x'\<in> S)"
  (is "?lhs \<longleftrightarrow> ?rhs")
proof
  assume ?lhs
  then show ?rhs
    unfolding openin_open open_dist by blast
next
  def T \<equiv> "{x. \<exists>a\<in>S. \<exists>d>0. (\<forall>y\<in>U. dist y a < d \<longrightarrow> y \<in> S) \<and> dist x a < d}"
  have 1: "\<forall>x\<in>T. \<exists>e>0. \<forall>y. dist y x < e \<longrightarrow> y \<in> T"
    unfolding T_def
    apply clarsimp
    apply (rule_tac x="d - dist x a" in exI)
    apply (clarsimp simp add: less_diff_eq)
    apply (erule rev_bexI)
    apply (rule_tac x=d in exI, clarify)
    apply (erule le_less_trans [OF dist_triangle])
    done
  assume ?rhs then have 2: "S = U \<inter> T"
    unfolding T_def
    apply auto
    apply (drule (1) bspec, erule rev_bexI)
    apply auto
    done
  from 1 2 show ?lhs
    unfolding openin_open open_dist by fast
qed

text {* These "transitivity" results are handy too *}

lemma openin_trans[trans]:
  "openin (subtopology euclidean T) S \<Longrightarrow> openin (subtopology euclidean U) T \<Longrightarrow>
    openin (subtopology euclidean U) S"
  unfolding open_openin openin_open by blast

lemma openin_open_trans: "openin (subtopology euclidean T) S \<Longrightarrow> open T \<Longrightarrow> open S"
  by (auto simp add: openin_open intro: openin_trans)

lemma closedin_trans[trans]:
  "closedin (subtopology euclidean T) S \<Longrightarrow> closedin (subtopology euclidean U) T \<Longrightarrow>
    closedin (subtopology euclidean U) S"
  by (auto simp add: closedin_closed closed_closedin closed_Inter Int_assoc)

lemma closedin_closed_trans: "closedin (subtopology euclidean T) S \<Longrightarrow> closed T \<Longrightarrow> closed S"
  by (auto simp add: closedin_closed intro: closedin_trans)


subsection {* Open and closed balls *}

definition ball :: "'a::metric_space \<Rightarrow> real \<Rightarrow> 'a set"
  where "ball x e = {y. dist x y < e}"

definition cball :: "'a::metric_space \<Rightarrow> real \<Rightarrow> 'a set"
  where "cball x e = {y. dist x y \<le> e}"

lemma mem_ball [simp]: "y \<in> ball x e \<longleftrightarrow> dist x y < e"
  by (simp add: ball_def)

lemma mem_cball [simp]: "y \<in> cball x e \<longleftrightarrow> dist x y \<le> e"
  by (simp add: cball_def)

lemma mem_ball_0:
  fixes x :: "'a::real_normed_vector"
  shows "x \<in> ball 0 e \<longleftrightarrow> norm x < e"
  by (simp add: dist_norm)

lemma mem_cball_0:
  fixes x :: "'a::real_normed_vector"
  shows "x \<in> cball 0 e \<longleftrightarrow> norm x \<le> e"
  by (simp add: dist_norm)

lemma centre_in_ball: "x \<in> ball x e \<longleftrightarrow> 0 < e"
  by simp

lemma centre_in_cball: "x \<in> cball x e \<longleftrightarrow> 0 \<le> e"
  by simp

lemma ball_subset_cball[simp,intro]: "ball x e \<subseteq> cball x e"
  by (simp add: subset_eq)

lemma subset_ball[intro]: "d \<le> e \<Longrightarrow> ball x d \<subseteq> ball x e"
  by (simp add: subset_eq)

lemma subset_cball[intro]: "d \<le> e \<Longrightarrow> cball x d \<subseteq> cball x e"
  by (simp add: subset_eq)

lemma ball_max_Un: "ball a (max r s) = ball a r \<union> ball a s"
  by (simp add: set_eq_iff) arith

lemma ball_min_Int: "ball a (min r s) = ball a r \<inter> ball a s"
  by (simp add: set_eq_iff)

lemma diff_less_iff:
  "(a::real) - b > 0 \<longleftrightarrow> a > b"
  "(a::real) - b < 0 \<longleftrightarrow> a < b"
  "a - b < c \<longleftrightarrow> a < c + b" "a - b > c \<longleftrightarrow> a > c + b"
  by arith+

lemma diff_le_iff:
  "(a::real) - b \<ge> 0 \<longleftrightarrow> a \<ge> b"
  "(a::real) - b \<le> 0 \<longleftrightarrow> a \<le> b"
  "a - b \<le> c \<longleftrightarrow> a \<le> c + b"
  "a - b \<ge> c \<longleftrightarrow> a \<ge> c + b"
  by arith+

lemma open_vimage: (* TODO: move to Topological_Spaces.thy *)
  assumes "open s" and "continuous_on UNIV f"
  shows "open (vimage f s)"
  using assms unfolding continuous_on_open_vimage [OF open_UNIV]
  by simp

lemma open_ball [intro, simp]: "open (ball x e)"
proof -
  have "open (dist x -` {..<e})"
    by (intro open_vimage open_lessThan continuous_on_intros)
  also have "dist x -` {..<e} = ball x e"
    by auto
  finally show ?thesis .
qed

lemma open_contains_ball: "open S \<longleftrightarrow> (\<forall>x\<in>S. \<exists>e>0. ball x e \<subseteq> S)"
  unfolding open_dist subset_eq mem_ball Ball_def dist_commute ..

lemma openE[elim?]:
  assumes "open S" "x\<in>S"
  obtains e where "e>0" "ball x e \<subseteq> S"
  using assms unfolding open_contains_ball by auto

lemma open_contains_ball_eq: "open S \<Longrightarrow> \<forall>x. x\<in>S \<longleftrightarrow> (\<exists>e>0. ball x e \<subseteq> S)"
  by (metis open_contains_ball subset_eq centre_in_ball)

lemma ball_eq_empty[simp]: "ball x e = {} \<longleftrightarrow> e \<le> 0"
  unfolding mem_ball set_eq_iff
  apply (simp add: not_less)
  apply (metis zero_le_dist order_trans dist_self)
  done

lemma ball_empty[intro]: "e \<le> 0 \<Longrightarrow> ball x e = {}" by simp

lemma euclidean_dist_l2:
  fixes x y :: "'a :: euclidean_space"
  shows "dist x y = setL2 (\<lambda>i. dist (x \<bullet> i) (y \<bullet> i)) Basis"
  unfolding dist_norm norm_eq_sqrt_inner setL2_def
  by (subst euclidean_inner) (simp add: power2_eq_square inner_diff_left)

definition (in euclidean_space) eucl_less (infix "<e" 50)
  where "eucl_less a b \<longleftrightarrow> (\<forall>i\<in>Basis. a \<bullet> i < b \<bullet> i)"

definition box_eucl_less: "box a b = {x. a <e x \<and> x <e b}"

lemma box_def: "box a b = {x. \<forall>i\<in>Basis. a \<bullet> i < x \<bullet> i \<and> x \<bullet> i < b \<bullet> i}"
  and in_box_eucl_less: "x \<in> box a b \<longleftrightarrow> a <e x \<and> x <e b"
  by (auto simp: box_eucl_less eucl_less_def)

lemma rational_boxes:
  fixes x :: "'a\<Colon>euclidean_space"
  assumes "e > 0"
  shows "\<exists>a b. (\<forall>i\<in>Basis. a \<bullet> i \<in> \<rat> \<and> b \<bullet> i \<in> \<rat> ) \<and> x \<in> box a b \<and> box a b \<subseteq> ball x e"
proof -
  def e' \<equiv> "e / (2 * sqrt (real (DIM ('a))))"
  then have e: "e' > 0"
    using assms by (auto intro!: divide_pos_pos simp: DIM_positive)
  have "\<forall>i. \<exists>y. y \<in> \<rat> \<and> y < x \<bullet> i \<and> x \<bullet> i - y < e'" (is "\<forall>i. ?th i")
  proof
    fix i
    from Rats_dense_in_real[of "x \<bullet> i - e'" "x \<bullet> i"] e
    show "?th i" by auto
  qed
  from choice[OF this] obtain a where
    a: "\<forall>xa. a xa \<in> \<rat> \<and> a xa < x \<bullet> xa \<and> x \<bullet> xa - a xa < e'" ..
  have "\<forall>i. \<exists>y. y \<in> \<rat> \<and> x \<bullet> i < y \<and> y - x \<bullet> i < e'" (is "\<forall>i. ?th i")
  proof
    fix i
    from Rats_dense_in_real[of "x \<bullet> i" "x \<bullet> i + e'"] e
    show "?th i" by auto
  qed
  from choice[OF this] obtain b where
    b: "\<forall>xa. b xa \<in> \<rat> \<and> x \<bullet> xa < b xa \<and> b xa - x \<bullet> xa < e'" ..
  let ?a = "\<Sum>i\<in>Basis. a i *\<^sub>R i" and ?b = "\<Sum>i\<in>Basis. b i *\<^sub>R i"
  show ?thesis
  proof (rule exI[of _ ?a], rule exI[of _ ?b], safe)
    fix y :: 'a
    assume *: "y \<in> box ?a ?b"
    have "dist x y = sqrt (\<Sum>i\<in>Basis. (dist (x \<bullet> i) (y \<bullet> i))\<^sup>2)"
      unfolding setL2_def[symmetric] by (rule euclidean_dist_l2)
    also have "\<dots> < sqrt (\<Sum>(i::'a)\<in>Basis. e^2 / real (DIM('a)))"
    proof (rule real_sqrt_less_mono, rule setsum_strict_mono)
      fix i :: "'a"
      assume i: "i \<in> Basis"
      have "a i < y\<bullet>i \<and> y\<bullet>i < b i"
        using * i by (auto simp: box_def)
      moreover have "a i < x\<bullet>i" "x\<bullet>i - a i < e'"
        using a by auto
      moreover have "x\<bullet>i < b i" "b i - x\<bullet>i < e'"
        using b by auto
      ultimately have "\<bar>x\<bullet>i - y\<bullet>i\<bar> < 2 * e'"
        by auto
      then have "dist (x \<bullet> i) (y \<bullet> i) < e/sqrt (real (DIM('a)))"
        unfolding e'_def by (auto simp: dist_real_def)
      then have "(dist (x \<bullet> i) (y \<bullet> i))\<^sup>2 < (e/sqrt (real (DIM('a))))\<^sup>2"
        by (rule power_strict_mono) auto
      then show "(dist (x \<bullet> i) (y \<bullet> i))\<^sup>2 < e\<^sup>2 / real DIM('a)"
        by (simp add: power_divide)
    qed auto
    also have "\<dots> = e"
      using `0 < e` by (simp add: real_eq_of_nat)
    finally show "y \<in> ball x e"
      by (auto simp: ball_def)
  qed (insert a b, auto simp: box_def)
qed

lemma open_UNION_box:
  fixes M :: "'a\<Colon>euclidean_space set"
  assumes "open M"
  defines "a' \<equiv> \<lambda>f :: 'a \<Rightarrow> real \<times> real. (\<Sum>(i::'a)\<in>Basis. fst (f i) *\<^sub>R i)"
  defines "b' \<equiv> \<lambda>f :: 'a \<Rightarrow> real \<times> real. (\<Sum>(i::'a)\<in>Basis. snd (f i) *\<^sub>R i)"
  defines "I \<equiv> {f\<in>Basis \<rightarrow>\<^sub>E \<rat> \<times> \<rat>. box (a' f) (b' f) \<subseteq> M}"
  shows "M = (\<Union>f\<in>I. box (a' f) (b' f))"
proof -
  {
    fix x assume "x \<in> M"
    obtain e where e: "e > 0" "ball x e \<subseteq> M"
      using openE[OF `open M` `x \<in> M`] by auto
    moreover obtain a b where ab:
      "x \<in> box a b"
      "\<forall>i \<in> Basis. a \<bullet> i \<in> \<rat>"
      "\<forall>i\<in>Basis. b \<bullet> i \<in> \<rat>"
      "box a b \<subseteq> ball x e"
      using rational_boxes[OF e(1)] by metis
    ultimately have "x \<in> (\<Union>f\<in>I. box (a' f) (b' f))"
       by (intro UN_I[of "\<lambda>i\<in>Basis. (a \<bullet> i, b \<bullet> i)"])
          (auto simp: euclidean_representation I_def a'_def b'_def)
  }
  then show ?thesis by (auto simp: I_def)
qed


subsection{* Connectedness *}

lemma connected_local:
 "connected S \<longleftrightarrow>
  \<not> (\<exists>e1 e2.
      openin (subtopology euclidean S) e1 \<and>
      openin (subtopology euclidean S) e2 \<and>
      S \<subseteq> e1 \<union> e2 \<and>
      e1 \<inter> e2 = {} \<and>
      e1 \<noteq> {} \<and>
      e2 \<noteq> {})"
  unfolding connected_def openin_open
  apply safe
  apply blast+
  done

lemma exists_diff:
  fixes P :: "'a set \<Rightarrow> bool"
  shows "(\<exists>S. P(- S)) \<longleftrightarrow> (\<exists>S. P S)" (is "?lhs \<longleftrightarrow> ?rhs")
proof -
  {
    assume "?lhs"
    then have ?rhs by blast
  }
  moreover
  {
    fix S
    assume H: "P S"
    have "S = - (- S)" by auto
    with H have "P (- (- S))" by metis
  }
  ultimately show ?thesis by metis
qed

lemma connected_clopen: "connected S \<longleftrightarrow>
  (\<forall>T. openin (subtopology euclidean S) T \<and>
     closedin (subtopology euclidean S) T \<longrightarrow> T = {} \<or> T = S)" (is "?lhs \<longleftrightarrow> ?rhs")
proof -
  have "\<not> connected S \<longleftrightarrow>
    (\<exists>e1 e2. open e1 \<and> open (- e2) \<and> S \<subseteq> e1 \<union> (- e2) \<and> e1 \<inter> (- e2) \<inter> S = {} \<and> e1 \<inter> S \<noteq> {} \<and> (- e2) \<inter> S \<noteq> {})"
    unfolding connected_def openin_open closedin_closed
    apply (subst exists_diff)
    apply blast
    done
  then have th0: "connected S \<longleftrightarrow>
    \<not> (\<exists>e2 e1. closed e2 \<and> open e1 \<and> S \<subseteq> e1 \<union> (- e2) \<and> e1 \<inter> (- e2) \<inter> S = {} \<and> e1 \<inter> S \<noteq> {} \<and> (- e2) \<inter> S \<noteq> {})"
    (is " _ \<longleftrightarrow> \<not> (\<exists>e2 e1. ?P e2 e1)")
    apply (simp add: closed_def)
    apply metis
    done
  have th1: "?rhs \<longleftrightarrow> \<not> (\<exists>t' t. closed t'\<and>t = S\<inter>t' \<and> t\<noteq>{} \<and> t\<noteq>S \<and> (\<exists>t'. open t' \<and> t = S \<inter> t'))"
    (is "_ \<longleftrightarrow> \<not> (\<exists>t' t. ?Q t' t)")
    unfolding connected_def openin_open closedin_closed by auto
  {
    fix e2
    {
      fix e1
      have "?P e2 e1 \<longleftrightarrow> (\<exists>t. closed e2 \<and> t = S\<inter>e2 \<and> open e1 \<and> t = S\<inter>e1 \<and> t\<noteq>{} \<and> t \<noteq> S)"
        by auto
    }
    then have "(\<exists>e1. ?P e2 e1) \<longleftrightarrow> (\<exists>t. ?Q e2 t)"
      by metis
  }
  then have "\<forall>e2. (\<exists>e1. ?P e2 e1) \<longleftrightarrow> (\<exists>t. ?Q e2 t)"
    by blast
  then show ?thesis
    unfolding th0 th1 by simp
qed


subsection{* Limit points *}

definition (in topological_space) islimpt:: "'a \<Rightarrow> 'a set \<Rightarrow> bool"  (infixr "islimpt" 60)
  where "x islimpt S \<longleftrightarrow> (\<forall>T. x\<in>T \<longrightarrow> open T \<longrightarrow> (\<exists>y\<in>S. y\<in>T \<and> y\<noteq>x))"

lemma islimptI:
  assumes "\<And>T. x \<in> T \<Longrightarrow> open T \<Longrightarrow> \<exists>y\<in>S. y \<in> T \<and> y \<noteq> x"
  shows "x islimpt S"
  using assms unfolding islimpt_def by auto

lemma islimptE:
  assumes "x islimpt S" and "x \<in> T" and "open T"
  obtains y where "y \<in> S" and "y \<in> T" and "y \<noteq> x"
  using assms unfolding islimpt_def by auto

lemma islimpt_iff_eventually: "x islimpt S \<longleftrightarrow> \<not> eventually (\<lambda>y. y \<notin> S) (at x)"
  unfolding islimpt_def eventually_at_topological by auto

lemma islimpt_subset: "x islimpt S \<Longrightarrow> S \<subseteq> T \<Longrightarrow> x islimpt T"
  unfolding islimpt_def by fast

lemma islimpt_approachable:
  fixes x :: "'a::metric_space"
  shows "x islimpt S \<longleftrightarrow> (\<forall>e>0. \<exists>x'\<in>S. x' \<noteq> x \<and> dist x' x < e)"
  unfolding islimpt_iff_eventually eventually_at by fast

lemma islimpt_approachable_le:
  fixes x :: "'a::metric_space"
  shows "x islimpt S \<longleftrightarrow> (\<forall>e>0. \<exists>x'\<in> S. x' \<noteq> x \<and> dist x' x \<le> e)"
  unfolding islimpt_approachable
  using approachable_lt_le [where f="\<lambda>y. dist y x" and P="\<lambda>y. y \<notin> S \<or> y = x",
    THEN arg_cong [where f=Not]]
  by (simp add: Bex_def conj_commute conj_left_commute)

lemma islimpt_UNIV_iff: "x islimpt UNIV \<longleftrightarrow> \<not> open {x}"
  unfolding islimpt_def by (safe, fast, case_tac "T = {x}", fast, fast)

lemma islimpt_punctured: "x islimpt S = x islimpt (S-{x})"
  unfolding islimpt_def by blast

text {* A perfect space has no isolated points. *}

lemma islimpt_UNIV [simp, intro]: "(x::'a::perfect_space) islimpt UNIV"
  unfolding islimpt_UNIV_iff by (rule not_open_singleton)

lemma perfect_choose_dist:
  fixes x :: "'a::{perfect_space, metric_space}"
  shows "0 < r \<Longrightarrow> \<exists>a. a \<noteq> x \<and> dist a x < r"
  using islimpt_UNIV [of x]
  by (simp add: islimpt_approachable)

lemma closed_limpt: "closed S \<longleftrightarrow> (\<forall>x. x islimpt S \<longrightarrow> x \<in> S)"
  unfolding closed_def
  apply (subst open_subopen)
  apply (simp add: islimpt_def subset_eq)
  apply (metis ComplE ComplI)
  done

lemma islimpt_EMPTY[simp]: "\<not> x islimpt {}"
  unfolding islimpt_def by auto

lemma finite_set_avoid:
  fixes a :: "'a::metric_space"
  assumes fS: "finite S"
  shows  "\<exists>d>0. \<forall>x\<in>S. x \<noteq> a \<longrightarrow> d \<le> dist a x"
proof (induct rule: finite_induct[OF fS])
  case 1
  then show ?case by (auto intro: zero_less_one)
next
  case (2 x F)
  from 2 obtain d where d: "d >0" "\<forall>x\<in>F. x\<noteq>a \<longrightarrow> d \<le> dist a x"
    by blast
  show ?case
  proof (cases "x = a")
    case True
    then show ?thesis using d by auto
  next
    case False
    let ?d = "min d (dist a x)"
    have dp: "?d > 0"
      using False d(1) using dist_nz by auto
    from d have d': "\<forall>x\<in>F. x\<noteq>a \<longrightarrow> ?d \<le> dist a x"
      by auto
    with dp False show ?thesis
      by (auto intro!: exI[where x="?d"])
  qed
qed

lemma islimpt_Un: "x islimpt (S \<union> T) \<longleftrightarrow> x islimpt S \<or> x islimpt T"
  by (simp add: islimpt_iff_eventually eventually_conj_iff)

lemma discrete_imp_closed:
  fixes S :: "'a::metric_space set"
  assumes e: "0 < e"
    and d: "\<forall>x \<in> S. \<forall>y \<in> S. dist y x < e \<longrightarrow> y = x"
  shows "closed S"
proof -
  {
    fix x
    assume C: "\<forall>e>0. \<exists>x'\<in>S. x' \<noteq> x \<and> dist x' x < e"
    from e have e2: "e/2 > 0" by arith
    from C[rule_format, OF e2] obtain y where y: "y \<in> S" "y \<noteq> x" "dist y x < e/2"
      by blast
    let ?m = "min (e/2) (dist x y) "
    from e2 y(2) have mp: "?m > 0"
      by (simp add: dist_nz[symmetric])
    from C[rule_format, OF mp] obtain z where z: "z \<in> S" "z \<noteq> x" "dist z x < ?m"
      by blast
    have th: "dist z y < e" using z y
      by (intro dist_triangle_lt [where z=x], simp)
    from d[rule_format, OF y(1) z(1) th] y z
    have False by (auto simp add: dist_commute)}
  then show ?thesis
    by (metis islimpt_approachable closed_limpt [where 'a='a])
qed


subsection {* Interior of a Set *}

definition "interior S = \<Union>{T. open T \<and> T \<subseteq> S}"

lemma interiorI [intro?]:
  assumes "open T" and "x \<in> T" and "T \<subseteq> S"
  shows "x \<in> interior S"
  using assms unfolding interior_def by fast

lemma interiorE [elim?]:
  assumes "x \<in> interior S"
  obtains T where "open T" and "x \<in> T" and "T \<subseteq> S"
  using assms unfolding interior_def by fast

lemma open_interior [simp, intro]: "open (interior S)"
  by (simp add: interior_def open_Union)

lemma interior_subset: "interior S \<subseteq> S"
  by (auto simp add: interior_def)

lemma interior_maximal: "T \<subseteq> S \<Longrightarrow> open T \<Longrightarrow> T \<subseteq> interior S"
  by (auto simp add: interior_def)

lemma interior_open: "open S \<Longrightarrow> interior S = S"
  by (intro equalityI interior_subset interior_maximal subset_refl)

lemma interior_eq: "interior S = S \<longleftrightarrow> open S"
  by (metis open_interior interior_open)

lemma open_subset_interior: "open S \<Longrightarrow> S \<subseteq> interior T \<longleftrightarrow> S \<subseteq> T"
  by (metis interior_maximal interior_subset subset_trans)

lemma interior_empty [simp]: "interior {} = {}"
  using open_empty by (rule interior_open)

lemma interior_UNIV [simp]: "interior UNIV = UNIV"
  using open_UNIV by (rule interior_open)

lemma interior_interior [simp]: "interior (interior S) = interior S"
  using open_interior by (rule interior_open)

lemma interior_mono: "S \<subseteq> T \<Longrightarrow> interior S \<subseteq> interior T"
  by (auto simp add: interior_def)

lemma interior_unique:
  assumes "T \<subseteq> S" and "open T"
  assumes "\<And>T'. T' \<subseteq> S \<Longrightarrow> open T' \<Longrightarrow> T' \<subseteq> T"
  shows "interior S = T"
  by (intro equalityI assms interior_subset open_interior interior_maximal)

lemma interior_inter [simp]: "interior (S \<inter> T) = interior S \<inter> interior T"
  by (intro equalityI Int_mono Int_greatest interior_mono Int_lower1
    Int_lower2 interior_maximal interior_subset open_Int open_interior)

lemma mem_interior: "x \<in> interior S \<longleftrightarrow> (\<exists>e>0. ball x e \<subseteq> S)"
  using open_contains_ball_eq [where S="interior S"]
  by (simp add: open_subset_interior)

lemma interior_limit_point [intro]:
  fixes x :: "'a::perfect_space"
  assumes x: "x \<in> interior S"
  shows "x islimpt S"
  using x islimpt_UNIV [of x]
  unfolding interior_def islimpt_def
  apply (clarsimp, rename_tac T T')
  apply (drule_tac x="T \<inter> T'" in spec)
  apply (auto simp add: open_Int)
  done

lemma interior_closed_Un_empty_interior:
  assumes cS: "closed S"
    and iT: "interior T = {}"
  shows "interior (S \<union> T) = interior S"
proof
  show "interior S \<subseteq> interior (S \<union> T)"
    by (rule interior_mono) (rule Un_upper1)
  show "interior (S \<union> T) \<subseteq> interior S"
  proof
    fix x
    assume "x \<in> interior (S \<union> T)"
    then obtain R where "open R" "x \<in> R" "R \<subseteq> S \<union> T" ..
    show "x \<in> interior S"
    proof (rule ccontr)
      assume "x \<notin> interior S"
      with `x \<in> R` `open R` obtain y where "y \<in> R - S"
        unfolding interior_def by fast
      from `open R` `closed S` have "open (R - S)"
        by (rule open_Diff)
      from `R \<subseteq> S \<union> T` have "R - S \<subseteq> T"
        by fast
      from `y \<in> R - S` `open (R - S)` `R - S \<subseteq> T` `interior T = {}` show False
        unfolding interior_def by fast
    qed
  qed
qed

lemma interior_Times: "interior (A \<times> B) = interior A \<times> interior B"
proof (rule interior_unique)
  show "interior A \<times> interior B \<subseteq> A \<times> B"
    by (intro Sigma_mono interior_subset)
  show "open (interior A \<times> interior B)"
    by (intro open_Times open_interior)
  fix T
  assume "T \<subseteq> A \<times> B" and "open T"
  then show "T \<subseteq> interior A \<times> interior B"
  proof safe
    fix x y
    assume "(x, y) \<in> T"
    then obtain C D where "open C" "open D" "C \<times> D \<subseteq> T" "x \<in> C" "y \<in> D"
      using `open T` unfolding open_prod_def by fast
    then have "open C" "open D" "C \<subseteq> A" "D \<subseteq> B" "x \<in> C" "y \<in> D"
      using `T \<subseteq> A \<times> B` by auto
    then show "x \<in> interior A" and "y \<in> interior B"
      by (auto intro: interiorI)
  qed
qed


subsection {* Closure of a Set *}

definition "closure S = S \<union> {x | x. x islimpt S}"

lemma interior_closure: "interior S = - (closure (- S))"
  unfolding interior_def closure_def islimpt_def by auto

lemma closure_interior: "closure S = - interior (- S)"
  unfolding interior_closure by simp

lemma closed_closure[simp, intro]: "closed (closure S)"
  unfolding closure_interior by (simp add: closed_Compl)

lemma closure_subset: "S \<subseteq> closure S"
  unfolding closure_def by simp

lemma closure_hull: "closure S = closed hull S"
  unfolding hull_def closure_interior interior_def by auto

lemma closure_eq: "closure S = S \<longleftrightarrow> closed S"
  unfolding closure_hull using closed_Inter by (rule hull_eq)

lemma closure_closed [simp]: "closed S \<Longrightarrow> closure S = S"
  unfolding closure_eq .

lemma closure_closure [simp]: "closure (closure S) = closure S"
  unfolding closure_hull by (rule hull_hull)

lemma closure_mono: "S \<subseteq> T \<Longrightarrow> closure S \<subseteq> closure T"
  unfolding closure_hull by (rule hull_mono)

lemma closure_minimal: "S \<subseteq> T \<Longrightarrow> closed T \<Longrightarrow> closure S \<subseteq> T"
  unfolding closure_hull by (rule hull_minimal)

lemma closure_unique:
  assumes "S \<subseteq> T"
    and "closed T"
    and "\<And>T'. S \<subseteq> T' \<Longrightarrow> closed T' \<Longrightarrow> T \<subseteq> T'"
  shows "closure S = T"
  using assms unfolding closure_hull by (rule hull_unique)

lemma closure_empty [simp]: "closure {} = {}"
  using closed_empty by (rule closure_closed)

lemma closure_UNIV [simp]: "closure UNIV = UNIV"
  using closed_UNIV by (rule closure_closed)

lemma closure_union [simp]: "closure (S \<union> T) = closure S \<union> closure T"
  unfolding closure_interior by simp

lemma closure_eq_empty: "closure S = {} \<longleftrightarrow> S = {}"
  using closure_empty closure_subset[of S]
  by blast

lemma closure_subset_eq: "closure S \<subseteq> S \<longleftrightarrow> closed S"
  using closure_eq[of S] closure_subset[of S]
  by simp

lemma open_inter_closure_eq_empty:
  "open S \<Longrightarrow> (S \<inter> closure T) = {} \<longleftrightarrow> S \<inter> T = {}"
  using open_subset_interior[of S "- T"]
  using interior_subset[of "- T"]
  unfolding closure_interior
  by auto

lemma open_inter_closure_subset:
  "open S \<Longrightarrow> (S \<inter> (closure T)) \<subseteq> closure(S \<inter> T)"
proof
  fix x
  assume as: "open S" "x \<in> S \<inter> closure T"
  {
    assume *: "x islimpt T"
    have "x islimpt (S \<inter> T)"
    proof (rule islimptI)
      fix A
      assume "x \<in> A" "open A"
      with as have "x \<in> A \<inter> S" "open (A \<inter> S)"
        by (simp_all add: open_Int)
      with * obtain y where "y \<in> T" "y \<in> A \<inter> S" "y \<noteq> x"
        by (rule islimptE)
      then have "y \<in> S \<inter> T" "y \<in> A \<and> y \<noteq> x"
        by simp_all
      then show "\<exists>y\<in>(S \<inter> T). y \<in> A \<and> y \<noteq> x" ..
    qed
  }
  then show "x \<in> closure (S \<inter> T)" using as
    unfolding closure_def
    by blast
qed

lemma closure_complement: "closure (- S) = - interior S"
  unfolding closure_interior by simp

lemma interior_complement: "interior (- S) = - closure S"
  unfolding closure_interior by simp

lemma closure_Times: "closure (A \<times> B) = closure A \<times> closure B"
proof (rule closure_unique)
  show "A \<times> B \<subseteq> closure A \<times> closure B"
    by (intro Sigma_mono closure_subset)
  show "closed (closure A \<times> closure B)"
    by (intro closed_Times closed_closure)
  fix T
  assume "A \<times> B \<subseteq> T" and "closed T"
  then show "closure A \<times> closure B \<subseteq> T"
    apply (simp add: closed_def open_prod_def, clarify)
    apply (rule ccontr)
    apply (drule_tac x="(a, b)" in bspec, simp, clarify, rename_tac C D)
    apply (simp add: closure_interior interior_def)
    apply (drule_tac x=C in spec)
    apply (drule_tac x=D in spec)
    apply auto
    done
qed

lemma islimpt_in_closure: "(x islimpt S) = (x:closure(S-{x}))"
  unfolding closure_def using islimpt_punctured by blast


subsection {* Frontier (aka boundary) *}

definition "frontier S = closure S - interior S"

lemma frontier_closed: "closed (frontier S)"
  by (simp add: frontier_def closed_Diff)

lemma frontier_closures: "frontier S = (closure S) \<inter> (closure(- S))"
  by (auto simp add: frontier_def interior_closure)

lemma frontier_straddle:
  fixes a :: "'a::metric_space"
  shows "a \<in> frontier S \<longleftrightarrow> (\<forall>e>0. (\<exists>x\<in>S. dist a x < e) \<and> (\<exists>x. x \<notin> S \<and> dist a x < e))"
  unfolding frontier_def closure_interior
  by (auto simp add: mem_interior subset_eq ball_def)

lemma frontier_subset_closed: "closed S \<Longrightarrow> frontier S \<subseteq> S"
  by (metis frontier_def closure_closed Diff_subset)

lemma frontier_empty[simp]: "frontier {} = {}"
  by (simp add: frontier_def)

lemma frontier_subset_eq: "frontier S \<subseteq> S \<longleftrightarrow> closed S"
proof-
  {
    assume "frontier S \<subseteq> S"
    then have "closure S \<subseteq> S"
      using interior_subset unfolding frontier_def by auto
    then have "closed S"
      using closure_subset_eq by auto
  }
  then show ?thesis using frontier_subset_closed[of S] ..
qed

lemma frontier_complement: "frontier(- S) = frontier S"
  by (auto simp add: frontier_def closure_complement interior_complement)

lemma frontier_disjoint_eq: "frontier S \<inter> S = {} \<longleftrightarrow> open S"
  using frontier_complement frontier_subset_eq[of "- S"]
  unfolding open_closed by auto

subsection {* Filters and the ``eventually true'' quantifier *}

definition indirection :: "'a::real_normed_vector \<Rightarrow> 'a \<Rightarrow> 'a filter"
    (infixr "indirection" 70)
  where "a indirection v = at a within {b. \<exists>c\<ge>0. b - a = scaleR c v}"

text {* Identify Trivial limits, where we can't approach arbitrarily closely. *}

lemma trivial_limit_within: "trivial_limit (at a within S) \<longleftrightarrow> \<not> a islimpt S"
proof
  assume "trivial_limit (at a within S)"
  then show "\<not> a islimpt S"
    unfolding trivial_limit_def
    unfolding eventually_at_topological
    unfolding islimpt_def
    apply (clarsimp simp add: set_eq_iff)
    apply (rename_tac T, rule_tac x=T in exI)
    apply (clarsimp, drule_tac x=y in bspec, simp_all)
    done
next
  assume "\<not> a islimpt S"
  then show "trivial_limit (at a within S)"
    unfolding trivial_limit_def
    unfolding eventually_at_topological
    unfolding islimpt_def
    apply clarsimp
    apply (rule_tac x=T in exI)
    apply auto
    done
qed

lemma trivial_limit_at_iff: "trivial_limit (at a) \<longleftrightarrow> \<not> a islimpt UNIV"
  using trivial_limit_within [of a UNIV] by simp

lemma trivial_limit_at:
  fixes a :: "'a::perfect_space"
  shows "\<not> trivial_limit (at a)"
  by (rule at_neq_bot)

lemma trivial_limit_at_infinity:
  "\<not> trivial_limit (at_infinity :: ('a::{real_normed_vector,perfect_space}) filter)"
  unfolding trivial_limit_def eventually_at_infinity
  apply clarsimp
  apply (subgoal_tac "\<exists>x::'a. x \<noteq> 0", clarify)
   apply (rule_tac x="scaleR (b / norm x) x" in exI, simp)
  apply (cut_tac islimpt_UNIV [of "0::'a", unfolded islimpt_def])
  apply (drule_tac x=UNIV in spec, simp)
  done

lemma not_trivial_limit_within: "\<not> trivial_limit (at x within S) = (x \<in> closure (S - {x}))"
  using islimpt_in_closure
  by (metis trivial_limit_within)

text {* Some property holds "sufficiently close" to the limit point. *}

lemma eventually_at2:
  "eventually P (at a) \<longleftrightarrow> (\<exists>d>0. \<forall>x. 0 < dist x a \<and> dist x a < d \<longrightarrow> P x)"
  unfolding eventually_at dist_nz by auto

lemma eventually_happens: "eventually P net \<Longrightarrow> trivial_limit net \<or> (\<exists>x. P x)"
  unfolding trivial_limit_def
  by (auto elim: eventually_rev_mp)

lemma trivial_limit_eventually: "trivial_limit net \<Longrightarrow> eventually P net"
  by simp

lemma trivial_limit_eq: "trivial_limit net \<longleftrightarrow> (\<forall>P. eventually P net)"
  by (simp add: filter_eq_iff)

text{* Combining theorems for "eventually" *}

lemma eventually_rev_mono:
  "eventually P net \<Longrightarrow> (\<forall>x. P x \<longrightarrow> Q x) \<Longrightarrow> eventually Q net"
  using eventually_mono [of P Q] by fast

lemma not_eventually: "(\<forall>x. \<not> P x ) \<Longrightarrow> \<not> trivial_limit net \<Longrightarrow> \<not> eventually (\<lambda>x. P x) net"
  by (simp add: eventually_False)


subsection {* Limits *}

lemma Lim:
  "(f ---> l) net \<longleftrightarrow>
        trivial_limit net \<or>
        (\<forall>e>0. eventually (\<lambda>x. dist (f x) l < e) net)"
  unfolding tendsto_iff trivial_limit_eq by auto

text{* Show that they yield usual definitions in the various cases. *}

lemma Lim_within_le: "(f ---> l)(at a within S) \<longleftrightarrow>
    (\<forall>e>0. \<exists>d>0. \<forall>x\<in>S. 0 < dist x a \<and> dist x a \<le> d \<longrightarrow> dist (f x) l < e)"
  by (auto simp add: tendsto_iff eventually_at_le dist_nz)

lemma Lim_within: "(f ---> l) (at a within S) \<longleftrightarrow>
    (\<forall>e >0. \<exists>d>0. \<forall>x \<in> S. 0 < dist x a \<and> dist x a  < d \<longrightarrow> dist (f x) l < e)"
  by (auto simp add: tendsto_iff eventually_at dist_nz)

lemma Lim_at: "(f ---> l) (at a) \<longleftrightarrow>
    (\<forall>e >0. \<exists>d>0. \<forall>x. 0 < dist x a \<and> dist x a < d  \<longrightarrow> dist (f x) l < e)"
  by (auto simp add: tendsto_iff eventually_at2)

lemma Lim_at_infinity:
  "(f ---> l) at_infinity \<longleftrightarrow> (\<forall>e>0. \<exists>b. \<forall>x. norm x \<ge> b \<longrightarrow> dist (f x) l < e)"
  by (auto simp add: tendsto_iff eventually_at_infinity)

lemma Lim_eventually: "eventually (\<lambda>x. f x = l) net \<Longrightarrow> (f ---> l) net"
  by (rule topological_tendstoI, auto elim: eventually_rev_mono)

text{* The expected monotonicity property. *}

lemma Lim_Un:
  assumes "(f ---> l) (at x within S)" "(f ---> l) (at x within T)"
  shows "(f ---> l) (at x within (S \<union> T))"
  using assms unfolding at_within_union by (rule filterlim_sup)

lemma Lim_Un_univ:
  "(f ---> l) (at x within S) \<Longrightarrow> (f ---> l) (at x within T) \<Longrightarrow>
    S \<union> T = UNIV \<Longrightarrow> (f ---> l) (at x)"
  by (metis Lim_Un)

text{* Interrelations between restricted and unrestricted limits. *}

lemma Lim_at_within: (* FIXME: rename *)
  "(f ---> l) (at x) \<Longrightarrow> (f ---> l) (at x within S)"
  by (metis order_refl filterlim_mono subset_UNIV at_le)

lemma eventually_within_interior:
  assumes "x \<in> interior S"
  shows "eventually P (at x within S) \<longleftrightarrow> eventually P (at x)"
  (is "?lhs = ?rhs")
proof
  from assms obtain T where T: "open T" "x \<in> T" "T \<subseteq> S" ..
  {
    assume "?lhs"
    then obtain A where "open A" and "x \<in> A" and "\<forall>y\<in>A. y \<noteq> x \<longrightarrow> y \<in> S \<longrightarrow> P y"
      unfolding eventually_at_topological
      by auto
    with T have "open (A \<inter> T)" and "x \<in> A \<inter> T" and "\<forall>y \<in> A \<inter> T. y \<noteq> x \<longrightarrow> P y"
      by auto
    then show "?rhs"
      unfolding eventually_at_topological by auto
  next
    assume "?rhs"
    then show "?lhs"
      by (auto elim: eventually_elim1 simp: eventually_at_filter)
  }
qed

lemma at_within_interior:
  "x \<in> interior S \<Longrightarrow> at x within S = at x"
  unfolding filter_eq_iff by (intro allI eventually_within_interior)

lemma Lim_within_LIMSEQ:
  fixes a :: "'a::first_countable_topology"
  assumes "\<forall>S. (\<forall>n. S n \<noteq> a \<and> S n \<in> T) \<and> S ----> a \<longrightarrow> (\<lambda>n. X (S n)) ----> L"
  shows "(X ---> L) (at a within T)"
  using assms unfolding tendsto_def [where l=L]
  by (simp add: sequentially_imp_eventually_within)

lemma Lim_right_bound:
  fixes f :: "'a :: {linorder_topology, conditionally_complete_linorder, no_top} \<Rightarrow>
    'b::{linorder_topology, conditionally_complete_linorder}"
  assumes mono: "\<And>a b. a \<in> I \<Longrightarrow> b \<in> I \<Longrightarrow> x < a \<Longrightarrow> a \<le> b \<Longrightarrow> f a \<le> f b"
    and bnd: "\<And>a. a \<in> I \<Longrightarrow> x < a \<Longrightarrow> K \<le> f a"
  shows "(f ---> Inf (f ` ({x<..} \<inter> I))) (at x within ({x<..} \<inter> I))"
proof (cases "{x<..} \<inter> I = {}")
  case True
  then show ?thesis by simp
next
  case False
  show ?thesis
  proof (rule order_tendstoI)
    fix a
    assume a: "a < Inf (f ` ({x<..} \<inter> I))"
    {
      fix y
      assume "y \<in> {x<..} \<inter> I"
      with False bnd have "Inf (f ` ({x<..} \<inter> I)) \<le> f y"
        by (auto intro!: cInf_lower bdd_belowI2)
      with a have "a < f y"
        by (blast intro: less_le_trans)
    }
    then show "eventually (\<lambda>x. a < f x) (at x within ({x<..} \<inter> I))"
      by (auto simp: eventually_at_filter intro: exI[of _ 1] zero_less_one)
  next
    fix a
    assume "Inf (f ` ({x<..} \<inter> I)) < a"
    from cInf_lessD[OF _ this] False obtain y where y: "x < y" "y \<in> I" "f y < a"
      by auto
    then have "eventually (\<lambda>x. x \<in> I \<longrightarrow> f x < a) (at_right x)"
      unfolding eventually_at_right by (metis less_imp_le le_less_trans mono)
    then show "eventually (\<lambda>x. f x < a) (at x within ({x<..} \<inter> I))"
      unfolding eventually_at_filter by eventually_elim simp
  qed
qed

text{* Another limit point characterization. *}

lemma islimpt_sequential:
  fixes x :: "'a::first_countable_topology"
  shows "x islimpt S \<longleftrightarrow> (\<exists>f. (\<forall>n::nat. f n \<in> S - {x}) \<and> (f ---> x) sequentially)"
    (is "?lhs = ?rhs")
proof
  assume ?lhs
  from countable_basis_at_decseq[of x] obtain A where A:
      "\<And>i. open (A i)"
      "\<And>i. x \<in> A i"
      "\<And>S. open S \<Longrightarrow> x \<in> S \<Longrightarrow> eventually (\<lambda>i. A i \<subseteq> S) sequentially"
    by blast
  def f \<equiv> "\<lambda>n. SOME y. y \<in> S \<and> y \<in> A n \<and> x \<noteq> y"
  {
    fix n
    from `?lhs` have "\<exists>y. y \<in> S \<and> y \<in> A n \<and> x \<noteq> y"
      unfolding islimpt_def using A(1,2)[of n] by auto
    then have "f n \<in> S \<and> f n \<in> A n \<and> x \<noteq> f n"
      unfolding f_def by (rule someI_ex)
    then have "f n \<in> S" "f n \<in> A n" "x \<noteq> f n" by auto
  }
  then have "\<forall>n. f n \<in> S - {x}" by auto
  moreover have "(\<lambda>n. f n) ----> x"
  proof (rule topological_tendstoI)
    fix S
    assume "open S" "x \<in> S"
    from A(3)[OF this] `\<And>n. f n \<in> A n`
    show "eventually (\<lambda>x. f x \<in> S) sequentially"
      by (auto elim!: eventually_elim1)
  qed
  ultimately show ?rhs by fast
next
  assume ?rhs
  then obtain f :: "nat \<Rightarrow> 'a" where f: "\<And>n. f n \<in> S - {x}" and lim: "f ----> x"
    by auto
  show ?lhs
    unfolding islimpt_def
  proof safe
    fix T
    assume "open T" "x \<in> T"
    from lim[THEN topological_tendstoD, OF this] f
    show "\<exists>y\<in>S. y \<in> T \<and> y \<noteq> x"
      unfolding eventually_sequentially by auto
  qed
qed

lemma Lim_null:
  fixes f :: "'a \<Rightarrow> 'b::real_normed_vector"
  shows "(f ---> l) net \<longleftrightarrow> ((\<lambda>x. f(x) - l) ---> 0) net"
  by (simp add: Lim dist_norm)

lemma Lim_null_comparison:
  fixes f :: "'a \<Rightarrow> 'b::real_normed_vector"
  assumes "eventually (\<lambda>x. norm (f x) \<le> g x) net" "(g ---> 0) net"
  shows "(f ---> 0) net"
  using assms(2)
proof (rule metric_tendsto_imp_tendsto)
  show "eventually (\<lambda>x. dist (f x) 0 \<le> dist (g x) 0) net"
    using assms(1) by (rule eventually_elim1) (simp add: dist_norm)
qed

lemma Lim_transform_bound:
  fixes f :: "'a \<Rightarrow> 'b::real_normed_vector"
    and g :: "'a \<Rightarrow> 'c::real_normed_vector"
  assumes "eventually (\<lambda>n. norm (f n) \<le> norm (g n)) net"
    and "(g ---> 0) net"
  shows "(f ---> 0) net"
  using assms(1) tendsto_norm_zero [OF assms(2)]
  by (rule Lim_null_comparison)

text{* Deducing things about the limit from the elements. *}

lemma Lim_in_closed_set:
  assumes "closed S"
    and "eventually (\<lambda>x. f(x) \<in> S) net"
    and "\<not> trivial_limit net" "(f ---> l) net"
  shows "l \<in> S"
proof (rule ccontr)
  assume "l \<notin> S"
  with `closed S` have "open (- S)" "l \<in> - S"
    by (simp_all add: open_Compl)
  with assms(4) have "eventually (\<lambda>x. f x \<in> - S) net"
    by (rule topological_tendstoD)
  with assms(2) have "eventually (\<lambda>x. False) net"
    by (rule eventually_elim2) simp
  with assms(3) show "False"
    by (simp add: eventually_False)
qed

text{* Need to prove closed(cball(x,e)) before deducing this as a corollary. *}

lemma Lim_dist_ubound:
  assumes "\<not>(trivial_limit net)"
    and "(f ---> l) net"
    and "eventually (\<lambda>x. dist a (f x) \<le> e) net"
  shows "dist a l \<le> e"
proof -
  have "dist a l \<in> {..e}"
  proof (rule Lim_in_closed_set)
    show "closed {..e}"
      by simp
    show "eventually (\<lambda>x. dist a (f x) \<in> {..e}) net"
      by (simp add: assms)
    show "\<not> trivial_limit net"
      by fact
    show "((\<lambda>x. dist a (f x)) ---> dist a l) net"
      by (intro tendsto_intros assms)
  qed
  then show ?thesis by simp
qed

lemma Lim_norm_ubound:
  fixes f :: "'a \<Rightarrow> 'b::real_normed_vector"
  assumes "\<not>(trivial_limit net)" "(f ---> l) net" "eventually (\<lambda>x. norm(f x) \<le> e) net"
  shows "norm(l) \<le> e"
proof -
  have "norm l \<in> {..e}"
  proof (rule Lim_in_closed_set)
    show "closed {..e}"
      by simp
    show "eventually (\<lambda>x. norm (f x) \<in> {..e}) net"
      by (simp add: assms)
    show "\<not> trivial_limit net"
      by fact
    show "((\<lambda>x. norm (f x)) ---> norm l) net"
      by (intro tendsto_intros assms)
  qed
  then show ?thesis by simp
qed

lemma Lim_norm_lbound:
  fixes f :: "'a \<Rightarrow> 'b::real_normed_vector"
  assumes "\<not> trivial_limit net"
    and "(f ---> l) net"
    and "eventually (\<lambda>x. e \<le> norm (f x)) net"
  shows "e \<le> norm l"
proof -
  have "norm l \<in> {e..}"
  proof (rule Lim_in_closed_set)
    show "closed {e..}"
      by simp
    show "eventually (\<lambda>x. norm (f x) \<in> {e..}) net"
      by (simp add: assms)
    show "\<not> trivial_limit net"
      by fact
    show "((\<lambda>x. norm (f x)) ---> norm l) net"
      by (intro tendsto_intros assms)
  qed
  then show ?thesis by simp
qed

text{* Limit under bilinear function *}

lemma Lim_bilinear:
  assumes "(f ---> l) net"
    and "(g ---> m) net"
    and "bounded_bilinear h"
  shows "((\<lambda>x. h (f x) (g x)) ---> (h l m)) net"
  using `bounded_bilinear h` `(f ---> l) net` `(g ---> m) net`
  by (rule bounded_bilinear.tendsto)

text{* These are special for limits out of the same vector space. *}

lemma Lim_within_id: "(id ---> a) (at a within s)"
  unfolding id_def by (rule tendsto_ident_at)

lemma Lim_at_id: "(id ---> a) (at a)"
  unfolding id_def by (rule tendsto_ident_at)

lemma Lim_at_zero:
  fixes a :: "'a::real_normed_vector"
    and l :: "'b::topological_space"
  shows "(f ---> l) (at a) \<longleftrightarrow> ((\<lambda>x. f(a + x)) ---> l) (at 0)"
  using LIM_offset_zero LIM_offset_zero_cancel ..

text{* It's also sometimes useful to extract the limit point from the filter. *}

abbreviation netlimit :: "'a::t2_space filter \<Rightarrow> 'a"
  where "netlimit F \<equiv> Lim F (\<lambda>x. x)"

lemma netlimit_within: "\<not> trivial_limit (at a within S) \<Longrightarrow> netlimit (at a within S) = a"
  by (rule tendsto_Lim) (auto intro: tendsto_intros)

lemma netlimit_at:
  fixes a :: "'a::{perfect_space,t2_space}"
  shows "netlimit (at a) = a"
  using netlimit_within [of a UNIV] by simp

lemma lim_within_interior:
  "x \<in> interior S \<Longrightarrow> (f ---> l) (at x within S) \<longleftrightarrow> (f ---> l) (at x)"
  by (metis at_within_interior)

lemma netlimit_within_interior:
  fixes x :: "'a::{t2_space,perfect_space}"
  assumes "x \<in> interior S"
  shows "netlimit (at x within S) = x"
  using assms by (metis at_within_interior netlimit_at)

text{* Transformation of limit. *}

lemma Lim_transform:
  fixes f g :: "'a::type \<Rightarrow> 'b::real_normed_vector"
  assumes "((\<lambda>x. f x - g x) ---> 0) net" "(f ---> l) net"
  shows "(g ---> l) net"
  using tendsto_diff [OF assms(2) assms(1)] by simp

lemma Lim_transform_eventually:
  "eventually (\<lambda>x. f x = g x) net \<Longrightarrow> (f ---> l) net \<Longrightarrow> (g ---> l) net"
  apply (rule topological_tendstoI)
  apply (drule (2) topological_tendstoD)
  apply (erule (1) eventually_elim2, simp)
  done

lemma Lim_transform_within:
  assumes "0 < d"
    and "\<forall>x'\<in>S. 0 < dist x' x \<and> dist x' x < d \<longrightarrow> f x' = g x'"
    and "(f ---> l) (at x within S)"
  shows "(g ---> l) (at x within S)"
proof (rule Lim_transform_eventually)
  show "eventually (\<lambda>x. f x = g x) (at x within S)"
    using assms(1,2) by (auto simp: dist_nz eventually_at)
  show "(f ---> l) (at x within S)" by fact
qed

lemma Lim_transform_at:
  assumes "0 < d"
    and "\<forall>x'. 0 < dist x' x \<and> dist x' x < d \<longrightarrow> f x' = g x'"
    and "(f ---> l) (at x)"
  shows "(g ---> l) (at x)"
  using _ assms(3)
proof (rule Lim_transform_eventually)
  show "eventually (\<lambda>x. f x = g x) (at x)"
    unfolding eventually_at2
    using assms(1,2) by auto
qed

text{* Common case assuming being away from some crucial point like 0. *}

lemma Lim_transform_away_within:
  fixes a b :: "'a::t1_space"
  assumes "a \<noteq> b"
    and "\<forall>x\<in>S. x \<noteq> a \<and> x \<noteq> b \<longrightarrow> f x = g x"
    and "(f ---> l) (at a within S)"
  shows "(g ---> l) (at a within S)"
proof (rule Lim_transform_eventually)
  show "(f ---> l) (at a within S)" by fact
  show "eventually (\<lambda>x. f x = g x) (at a within S)"
    unfolding eventually_at_topological
    by (rule exI [where x="- {b}"], simp add: open_Compl assms)
qed

lemma Lim_transform_away_at:
  fixes a b :: "'a::t1_space"
  assumes ab: "a\<noteq>b"
    and fg: "\<forall>x. x \<noteq> a \<and> x \<noteq> b \<longrightarrow> f x = g x"
    and fl: "(f ---> l) (at a)"
  shows "(g ---> l) (at a)"
  using Lim_transform_away_within[OF ab, of UNIV f g l] fg fl by simp

text{* Alternatively, within an open set. *}

lemma Lim_transform_within_open:
  assumes "open S" and "a \<in> S"
    and "\<forall>x\<in>S. x \<noteq> a \<longrightarrow> f x = g x"
    and "(f ---> l) (at a)"
  shows "(g ---> l) (at a)"
proof (rule Lim_transform_eventually)
  show "eventually (\<lambda>x. f x = g x) (at a)"
    unfolding eventually_at_topological
    using assms(1,2,3) by auto
  show "(f ---> l) (at a)" by fact
qed

text{* A congruence rule allowing us to transform limits assuming not at point. *}

(* FIXME: Only one congruence rule for tendsto can be used at a time! *)

lemma Lim_cong_within(*[cong add]*):
  assumes "a = b"
    and "x = y"
    and "S = T"
    and "\<And>x. x \<noteq> b \<Longrightarrow> x \<in> T \<Longrightarrow> f x = g x"
  shows "(f ---> x) (at a within S) \<longleftrightarrow> (g ---> y) (at b within T)"
  unfolding tendsto_def eventually_at_topological
  using assms by simp

lemma Lim_cong_at(*[cong add]*):
  assumes "a = b" "x = y"
    and "\<And>x. x \<noteq> a \<Longrightarrow> f x = g x"
  shows "((\<lambda>x. f x) ---> x) (at a) \<longleftrightarrow> ((g ---> y) (at a))"
  unfolding tendsto_def eventually_at_topological
  using assms by simp

text{* Useful lemmas on closure and set of possible sequential limits.*}

lemma closure_sequential:
  fixes l :: "'a::first_countable_topology"
  shows "l \<in> closure S \<longleftrightarrow> (\<exists>x. (\<forall>n. x n \<in> S) \<and> (x ---> l) sequentially)"
  (is "?lhs = ?rhs")
proof
  assume "?lhs"
  moreover
  {
    assume "l \<in> S"
    then have "?rhs" using tendsto_const[of l sequentially] by auto
  }
  moreover
  {
    assume "l islimpt S"
    then have "?rhs" unfolding islimpt_sequential by auto
  }
  ultimately show "?rhs"
    unfolding closure_def by auto
next
  assume "?rhs"
  then show "?lhs" unfolding closure_def islimpt_sequential by auto
qed

lemma closed_sequential_limits:
  fixes S :: "'a::first_countable_topology set"
  shows "closed S \<longleftrightarrow> (\<forall>x l. (\<forall>n. x n \<in> S) \<and> (x ---> l) sequentially \<longrightarrow> l \<in> S)"
  using closure_sequential [where 'a='a] closure_closed [where 'a='a]
    closed_limpt [where 'a='a] islimpt_sequential [where 'a='a] mem_delete [where 'a='a]
  by metis

lemma closure_approachable:
  fixes S :: "'a::metric_space set"
  shows "x \<in> closure S \<longleftrightarrow> (\<forall>e>0. \<exists>y\<in>S. dist y x < e)"
  apply (auto simp add: closure_def islimpt_approachable)
  apply (metis dist_self)
  done

lemma closed_approachable:
  fixes S :: "'a::metric_space set"
  shows "closed S \<Longrightarrow> (\<forall>e>0. \<exists>y\<in>S. dist y x < e) \<longleftrightarrow> x \<in> S"
  by (metis closure_closed closure_approachable)

lemma closure_contains_Inf:
  fixes S :: "real set"
  assumes "S \<noteq> {}" "bdd_below S"
  shows "Inf S \<in> closure S"
proof -
  have *: "\<forall>x\<in>S. Inf S \<le> x"
    using cInf_lower[of _ S] assms by metis
  {
    fix e :: real
    assume "e > 0"
    then have "Inf S < Inf S + e" by simp
    with assms obtain x where "x \<in> S" "x < Inf S + e"
      by (subst (asm) cInf_less_iff) auto
    with * have "\<exists>x\<in>S. dist x (Inf S) < e"
      by (intro bexI[of _ x]) (auto simp add: dist_real_def)
  }
  then show ?thesis unfolding closure_approachable by auto
qed

lemma closed_contains_Inf:
  fixes S :: "real set"
  shows "S \<noteq> {} \<Longrightarrow> bdd_below S \<Longrightarrow> closed S \<Longrightarrow> Inf S \<in> S"
  by (metis closure_contains_Inf closure_closed assms)

lemma not_trivial_limit_within_ball:
  "\<not> trivial_limit (at x within S) \<longleftrightarrow> (\<forall>e>0. S \<inter> ball x e - {x} \<noteq> {})"
  (is "?lhs = ?rhs")
proof -
  {
    assume "?lhs"
    {
      fix e :: real
      assume "e > 0"
      then obtain y where "y \<in> S - {x}" and "dist y x < e"
        using `?lhs` not_trivial_limit_within[of x S] closure_approachable[of x "S - {x}"]
        by auto
      then have "y \<in> S \<inter> ball x e - {x}"
        unfolding ball_def by (simp add: dist_commute)
      then have "S \<inter> ball x e - {x} \<noteq> {}" by blast
    }
    then have "?rhs" by auto
  }
  moreover
  {
    assume "?rhs"
    {
      fix e :: real
      assume "e > 0"
      then obtain y where "y \<in> S \<inter> ball x e - {x}"
        using `?rhs` by blast
      then have "y \<in> S - {x}" and "dist y x < e"
        unfolding ball_def by (simp_all add: dist_commute)
      then have "\<exists>y \<in> S - {x}. dist y x < e"
        by auto
    }
    then have "?lhs"
      using not_trivial_limit_within[of x S] closure_approachable[of x "S - {x}"]
      by auto
  }
  ultimately show ?thesis by auto
qed


subsection {* Infimum Distance *}

definition "infdist x A = (if A = {} then 0 else INF a:A. dist x a)"

lemma bdd_below_infdist[intro, simp]: "bdd_below (dist x`A)"
  by (auto intro!: zero_le_dist)

lemma infdist_notempty: "A \<noteq> {} \<Longrightarrow> infdist x A = (INF a:A. dist x a)"
  by (simp add: infdist_def)

lemma infdist_nonneg: "0 \<le> infdist x A"
  by (auto simp add: infdist_def intro: cINF_greatest)

lemma infdist_le: "a \<in> A \<Longrightarrow> infdist x A \<le> dist x a"
  by (auto intro: cINF_lower simp add: infdist_def)

lemma infdist_le2: "a \<in> A \<Longrightarrow> dist x a \<le> d \<Longrightarrow> infdist x A \<le> d"
  by (auto intro!: cINF_lower2 simp add: infdist_def)

lemma infdist_zero[simp]: "a \<in> A \<Longrightarrow> infdist a A = 0"
  by (auto intro!: antisym infdist_nonneg infdist_le2)

lemma infdist_triangle: "infdist x A \<le> infdist y A + dist x y"
proof (cases "A = {}")
  case True
  then show ?thesis by (simp add: infdist_def)
next
  case False
  then obtain a where "a \<in> A" by auto
  have "infdist x A \<le> Inf {dist x y + dist y a |a. a \<in> A}"
  proof (rule cInf_greatest)
    from `A \<noteq> {}` show "{dist x y + dist y a |a. a \<in> A} \<noteq> {}"
      by simp
    fix d
    assume "d \<in> {dist x y + dist y a |a. a \<in> A}"
    then obtain a where d: "d = dist x y + dist y a" "a \<in> A"
      by auto
    show "infdist x A \<le> d"
      unfolding infdist_notempty[OF `A \<noteq> {}`]
    proof (rule cINF_lower2)
      show "a \<in> A" by fact
      show "dist x a \<le> d"
        unfolding d by (rule dist_triangle)
    qed simp
  qed
  also have "\<dots> = dist x y + infdist y A"
  proof (rule cInf_eq, safe)
    fix a
    assume "a \<in> A"
    then show "dist x y + infdist y A \<le> dist x y + dist y a"
      by (auto intro: infdist_le)
  next
    fix i
    assume inf: "\<And>d. d \<in> {dist x y + dist y a |a. a \<in> A} \<Longrightarrow> i \<le> d"
    then have "i - dist x y \<le> infdist y A"
      unfolding infdist_notempty[OF `A \<noteq> {}`] using `a \<in> A`
      by (intro cINF_greatest) (auto simp: field_simps)
    then show "i \<le> dist x y + infdist y A"
      by simp
  qed
  finally show ?thesis by simp
qed

lemma in_closure_iff_infdist_zero:
  assumes "A \<noteq> {}"
  shows "x \<in> closure A \<longleftrightarrow> infdist x A = 0"
proof
  assume "x \<in> closure A"
  show "infdist x A = 0"
  proof (rule ccontr)
    assume "infdist x A \<noteq> 0"
    with infdist_nonneg[of x A] have "infdist x A > 0"
      by auto
    then have "ball x (infdist x A) \<inter> closure A = {}"
      apply auto
      apply (metis `x \<in> closure A` closure_approachable dist_commute infdist_le not_less)
      done
    then have "x \<notin> closure A"
      by (metis `0 < infdist x A` centre_in_ball disjoint_iff_not_equal)
    then show False using `x \<in> closure A` by simp
  qed
next
  assume x: "infdist x A = 0"
  then obtain a where "a \<in> A"
    by atomize_elim (metis all_not_in_conv assms)
  show "x \<in> closure A"
    unfolding closure_approachable
    apply safe
  proof (rule ccontr)
    fix e :: real
    assume "e > 0"
    assume "\<not> (\<exists>y\<in>A. dist y x < e)"
    then have "infdist x A \<ge> e" using `a \<in> A`
      unfolding infdist_def
      by (force simp: dist_commute intro: cINF_greatest)
    with x `e > 0` show False by auto
  qed
qed

lemma in_closed_iff_infdist_zero:
  assumes "closed A" "A \<noteq> {}"
  shows "x \<in> A \<longleftrightarrow> infdist x A = 0"
proof -
  have "x \<in> closure A \<longleftrightarrow> infdist x A = 0"
    by (rule in_closure_iff_infdist_zero) fact
  with assms show ?thesis by simp
qed

lemma tendsto_infdist [tendsto_intros]:
  assumes f: "(f ---> l) F"
  shows "((\<lambda>x. infdist (f x) A) ---> infdist l A) F"
proof (rule tendstoI)
  fix e ::real
  assume "e > 0"
  from tendstoD[OF f this]
  show "eventually (\<lambda>x. dist (infdist (f x) A) (infdist l A) < e) F"
  proof (eventually_elim)
    fix x
    from infdist_triangle[of l A "f x"] infdist_triangle[of "f x" A l]
    have "dist (infdist (f x) A) (infdist l A) \<le> dist (f x) l"
      by (simp add: dist_commute dist_real_def)
    also assume "dist (f x) l < e"
    finally show "dist (infdist (f x) A) (infdist l A) < e" .
  qed
qed

text{* Some other lemmas about sequences. *}

lemma sequentially_offset: (* TODO: move to Topological_Spaces.thy *)
  assumes "eventually (\<lambda>i. P i) sequentially"
  shows "eventually (\<lambda>i. P (i + k)) sequentially"
  using assms by (rule eventually_sequentially_seg [THEN iffD2])

lemma seq_offset_neg: (* TODO: move to Topological_Spaces.thy *)
  "(f ---> l) sequentially \<Longrightarrow> ((\<lambda>i. f(i - k)) ---> l) sequentially"
  apply (erule filterlim_compose)
  apply (simp add: filterlim_def le_sequentially eventually_filtermap eventually_sequentially)
  apply arith
  done

lemma seq_harmonic: "((\<lambda>n. inverse (real n)) ---> 0) sequentially"
  using LIMSEQ_inverse_real_of_nat by (rule LIMSEQ_imp_Suc) (* TODO: move to Limits.thy *)

subsection {* More properties of closed balls *}

lemma closed_vimage: (* TODO: move to Topological_Spaces.thy *)
  assumes "closed s" and "continuous_on UNIV f"
  shows "closed (vimage f s)"
  using assms unfolding continuous_on_closed_vimage [OF closed_UNIV]
  by simp

lemma closed_cball: "closed (cball x e)"
proof -
  have "closed (dist x -` {..e})"
    by (intro closed_vimage closed_atMost continuous_on_intros)
  also have "dist x -` {..e} = cball x e"
    by auto
  finally show ?thesis .
qed

lemma open_contains_cball: "open S \<longleftrightarrow> (\<forall>x\<in>S. \<exists>e>0.  cball x e \<subseteq> S)"
proof -
  {
    fix x and e::real
    assume "x\<in>S" "e>0" "ball x e \<subseteq> S"
    then have "\<exists>d>0. cball x d \<subseteq> S" unfolding subset_eq by (rule_tac x="e/2" in exI, auto)
  }
  moreover
  {
    fix x and e::real
    assume "x\<in>S" "e>0" "cball x e \<subseteq> S"
    then have "\<exists>d>0. ball x d \<subseteq> S"
      unfolding subset_eq
      apply(rule_tac x="e/2" in exI)
      apply auto
      done
  }
  ultimately show ?thesis
    unfolding open_contains_ball by auto
qed

lemma open_contains_cball_eq: "open S \<Longrightarrow> (\<forall>x. x \<in> S \<longleftrightarrow> (\<exists>e>0. cball x e \<subseteq> S))"
  by (metis open_contains_cball subset_eq order_less_imp_le centre_in_cball)

lemma mem_interior_cball: "x \<in> interior S \<longleftrightarrow> (\<exists>e>0. cball x e \<subseteq> S)"
  apply (simp add: interior_def, safe)
  apply (force simp add: open_contains_cball)
  apply (rule_tac x="ball x e" in exI)
  apply (simp add: subset_trans [OF ball_subset_cball])
  done

lemma islimpt_ball:
  fixes x y :: "'a::{real_normed_vector,perfect_space}"
  shows "y islimpt ball x e \<longleftrightarrow> 0 < e \<and> y \<in> cball x e"
  (is "?lhs = ?rhs")
proof
  assume "?lhs"
  {
    assume "e \<le> 0"
    then have *:"ball x e = {}"
      using ball_eq_empty[of x e] by auto
    have False using `?lhs`
      unfolding * using islimpt_EMPTY[of y] by auto
  }
  then have "e > 0" by (metis not_less)
  moreover
  have "y \<in> cball x e"
    using closed_cball[of x e] islimpt_subset[of y "ball x e" "cball x e"]
      ball_subset_cball[of x e] `?lhs`
    unfolding closed_limpt by auto
  ultimately show "?rhs" by auto
next
  assume "?rhs"
  then have "e > 0" by auto
  {
    fix d :: real
    assume "d > 0"
    have "\<exists>x'\<in>ball x e. x' \<noteq> y \<and> dist x' y < d"
    proof (cases "d \<le> dist x y")
      case True
      then show "\<exists>x'\<in>ball x e. x' \<noteq> y \<and> dist x' y < d"
      proof (cases "x = y")
        case True
        then have False
          using `d \<le> dist x y` `d>0` by auto
        then show "\<exists>x'\<in>ball x e. x' \<noteq> y \<and> dist x' y < d"
          by auto
      next
        case False
        have "dist x (y - (d / (2 * dist y x)) *\<^sub>R (y - x)) =
          norm (x - y + (d / (2 * norm (y - x))) *\<^sub>R (y - x))"
          unfolding mem_cball mem_ball dist_norm diff_diff_eq2 diff_add_eq[symmetric]
          by auto
        also have "\<dots> = \<bar>- 1 + d / (2 * norm (x - y))\<bar> * norm (x - y)"
          using scaleR_left_distrib[of "- 1" "d / (2 * norm (y - x))", symmetric, of "y - x"]
          unfolding scaleR_minus_left scaleR_one
          by (auto simp add: norm_minus_commute)
        also have "\<dots> = \<bar>- norm (x - y) + d / 2\<bar>"
          unfolding abs_mult_pos[of "norm (x - y)", OF norm_ge_zero[of "x - y"]]
          unfolding distrib_right using `x\<noteq>y`[unfolded dist_nz, unfolded dist_norm]
          by auto
        also have "\<dots> \<le> e - d/2" using `d \<le> dist x y` and `d>0` and `?rhs`
          by (auto simp add: dist_norm)
        finally have "y - (d / (2 * dist y x)) *\<^sub>R (y - x) \<in> ball x e" using `d>0`
          by auto
        moreover
        have "(d / (2*dist y x)) *\<^sub>R (y - x) \<noteq> 0"
          using `x\<noteq>y`[unfolded dist_nz] `d>0` unfolding scaleR_eq_0_iff
          by (auto simp add: dist_commute)
        moreover
        have "dist (y - (d / (2 * dist y x)) *\<^sub>R (y - x)) y < d"
          unfolding dist_norm
          apply simp
          unfolding norm_minus_cancel
          using `d > 0` `x\<noteq>y`[unfolded dist_nz] dist_commute[of x y]
          unfolding dist_norm
          apply auto
          done
        ultimately show "\<exists>x'\<in>ball x e. x' \<noteq> y \<and> dist x' y < d"
          apply (rule_tac x = "y - (d / (2*dist y x)) *\<^sub>R (y - x)" in bexI)
          apply auto
          done
      qed
    next
      case False
      then have "d > dist x y" by auto
      show "\<exists>x' \<in> ball x e. x' \<noteq> y \<and> dist x' y < d"
      proof (cases "x = y")
        case True
        obtain z where **: "z \<noteq> y" "dist z y < min e d"
          using perfect_choose_dist[of "min e d" y]
          using `d > 0` `e>0` by auto
        show "\<exists>x'\<in>ball x e. x' \<noteq> y \<and> dist x' y < d"
          unfolding `x = y`
          using `z \<noteq> y` **
          apply (rule_tac x=z in bexI)
          apply (auto simp add: dist_commute)
          done
      next
        case False
        then show "\<exists>x'\<in>ball x e. x' \<noteq> y \<and> dist x' y < d"
          using `d>0` `d > dist x y` `?rhs`
          apply (rule_tac x=x in bexI)
          apply auto
          done
      qed
    qed
  }
  then show "?lhs"
    unfolding mem_cball islimpt_approachable mem_ball by auto
qed

lemma closure_ball_lemma:
  fixes x y :: "'a::real_normed_vector"
  assumes "x \<noteq> y"
  shows "y islimpt ball x (dist x y)"
proof (rule islimptI)
  fix T
  assume "y \<in> T" "open T"
  then obtain r where "0 < r" "\<forall>z. dist z y < r \<longrightarrow> z \<in> T"
    unfolding open_dist by fast
  (* choose point between x and y, within distance r of y. *)
  def k \<equiv> "min 1 (r / (2 * dist x y))"
  def z \<equiv> "y + scaleR k (x - y)"
  have z_def2: "z = x + scaleR (1 - k) (y - x)"
    unfolding z_def by (simp add: algebra_simps)
  have "dist z y < r"
    unfolding z_def k_def using `0 < r`
    by (simp add: dist_norm min_def)
  then have "z \<in> T"
    using `\<forall>z. dist z y < r \<longrightarrow> z \<in> T` by simp
  have "dist x z < dist x y"
    unfolding z_def2 dist_norm
    apply (simp add: norm_minus_commute)
    apply (simp only: dist_norm [symmetric])
    apply (subgoal_tac "\<bar>1 - k\<bar> * dist x y < 1 * dist x y", simp)
    apply (rule mult_strict_right_mono)
    apply (simp add: k_def divide_pos_pos zero_less_dist_iff `0 < r` `x \<noteq> y`)
    apply (simp add: zero_less_dist_iff `x \<noteq> y`)
    done
  then have "z \<in> ball x (dist x y)"
    by simp
  have "z \<noteq> y"
    unfolding z_def k_def using `x \<noteq> y` `0 < r`
    by (simp add: min_def)
  show "\<exists>z\<in>ball x (dist x y). z \<in> T \<and> z \<noteq> y"
    using `z \<in> ball x (dist x y)` `z \<in> T` `z \<noteq> y`
    by fast
qed

lemma closure_ball:
  fixes x :: "'a::real_normed_vector"
  shows "0 < e \<Longrightarrow> closure (ball x e) = cball x e"
  apply (rule equalityI)
  apply (rule closure_minimal)
  apply (rule ball_subset_cball)
  apply (rule closed_cball)
  apply (rule subsetI, rename_tac y)
  apply (simp add: le_less [where 'a=real])
  apply (erule disjE)
  apply (rule subsetD [OF closure_subset], simp)
  apply (simp add: closure_def)
  apply clarify
  apply (rule closure_ball_lemma)
  apply (simp add: zero_less_dist_iff)
  done

(* In a trivial vector space, this fails for e = 0. *)
lemma interior_cball:
  fixes x :: "'a::{real_normed_vector, perfect_space}"
  shows "interior (cball x e) = ball x e"
proof (cases "e \<ge> 0")
  case False note cs = this
  from cs have "ball x e = {}"
    using ball_empty[of e x] by auto
  moreover
  {
    fix y
    assume "y \<in> cball x e"
    then have False
      unfolding mem_cball using dist_nz[of x y] cs by auto
  }
  then have "cball x e = {}" by auto
  then have "interior (cball x e) = {}"
    using interior_empty by auto
  ultimately show ?thesis by blast
next
  case True note cs = this
  have "ball x e \<subseteq> cball x e"
    using ball_subset_cball by auto
  moreover
  {
    fix S y
    assume as: "S \<subseteq> cball x e" "open S" "y\<in>S"
    then obtain d where "d>0" and d: "\<forall>x'. dist x' y < d \<longrightarrow> x' \<in> S"
      unfolding open_dist by blast
    then obtain xa where xa_y: "xa \<noteq> y" and xa: "dist xa y < d"
      using perfect_choose_dist [of d] by auto
    have "xa \<in> S"
      using d[THEN spec[where x = xa]]
      using xa by (auto simp add: dist_commute)
    then have xa_cball: "xa \<in> cball x e"
      using as(1) by auto
    then have "y \<in> ball x e"
    proof (cases "x = y")
      case True
      then have "e > 0"
        using xa_y[unfolded dist_nz] xa_cball[unfolded mem_cball]
        by (auto simp add: dist_commute)
      then show "y \<in> ball x e"
        using `x = y ` by simp
    next
      case False
      have "dist (y + (d / 2 / dist y x) *\<^sub>R (y - x)) y < d"
        unfolding dist_norm
        using `d>0` norm_ge_zero[of "y - x"] `x \<noteq> y` by auto
      then have *: "y + (d / 2 / dist y x) *\<^sub>R (y - x) \<in> cball x e"
        using d as(1)[unfolded subset_eq] by blast
      have "y - x \<noteq> 0" using `x \<noteq> y` by auto
      then have **:"d / (2 * norm (y - x)) > 0"
        unfolding zero_less_norm_iff[symmetric]
        using `d>0` divide_pos_pos[of d "2*norm (y - x)"] by auto
      have "dist (y + (d / 2 / dist y x) *\<^sub>R (y - x)) x =
        norm (y + (d / (2 * norm (y - x))) *\<^sub>R y - (d / (2 * norm (y - x))) *\<^sub>R x - x)"
        by (auto simp add: dist_norm algebra_simps)
      also have "\<dots> = norm ((1 + d / (2 * norm (y - x))) *\<^sub>R (y - x))"
        by (auto simp add: algebra_simps)
      also have "\<dots> = \<bar>1 + d / (2 * norm (y - x))\<bar> * norm (y - x)"
        using ** by auto
      also have "\<dots> = (dist y x) + d/2"
        using ** by (auto simp add: distrib_right dist_norm)
      finally have "e \<ge> dist x y +d/2"
        using *[unfolded mem_cball] by (auto simp add: dist_commute)
      then show "y \<in> ball x e"
        unfolding mem_ball using `d>0` by auto
    qed
  }
  then have "\<forall>S \<subseteq> cball x e. open S \<longrightarrow> S \<subseteq> ball x e"
    by auto
  ultimately show ?thesis
    using interior_unique[of "ball x e" "cball x e"]
    using open_ball[of x e]
    by auto
qed

lemma frontier_ball:
  fixes a :: "'a::real_normed_vector"
  shows "0 < e \<Longrightarrow> frontier(ball a e) = {x. dist a x = e}"
  apply (simp add: frontier_def closure_ball interior_open order_less_imp_le)
  apply (simp add: set_eq_iff)
  apply arith
  done

lemma frontier_cball:
  fixes a :: "'a::{real_normed_vector, perfect_space}"
  shows "frontier (cball a e) = {x. dist a x = e}"
  apply (simp add: frontier_def interior_cball closed_cball order_less_imp_le)
  apply (simp add: set_eq_iff)
  apply arith
  done

lemma cball_eq_empty: "cball x e = {} \<longleftrightarrow> e < 0"
  apply (simp add: set_eq_iff not_le)
  apply (metis zero_le_dist dist_self order_less_le_trans)
  done

lemma cball_empty: "e < 0 \<Longrightarrow> cball x e = {}"
  by (simp add: cball_eq_empty)

lemma cball_eq_sing:
  fixes x :: "'a::{metric_space,perfect_space}"
  shows "cball x e = {x} \<longleftrightarrow> e = 0"
proof (rule linorder_cases)
  assume e: "0 < e"
  obtain a where "a \<noteq> x" "dist a x < e"
    using perfect_choose_dist [OF e] by auto
  then have "a \<noteq> x" "dist x a \<le> e"
    by (auto simp add: dist_commute)
  with e show ?thesis by (auto simp add: set_eq_iff)
qed auto

lemma cball_sing:
  fixes x :: "'a::metric_space"
  shows "e = 0 \<Longrightarrow> cball x e = {x}"
  by (auto simp add: set_eq_iff)


subsection {* Boundedness *}

  (* FIXME: This has to be unified with BSEQ!! *)
definition (in metric_space) bounded :: "'a set \<Rightarrow> bool"
  where "bounded S \<longleftrightarrow> (\<exists>x e. \<forall>y\<in>S. dist x y \<le> e)"

lemma bounded_subset_cball: "bounded S \<longleftrightarrow> (\<exists>e x. S \<subseteq> cball x e)"
  unfolding bounded_def subset_eq by auto

lemma bounded_any_center: "bounded S \<longleftrightarrow> (\<exists>e. \<forall>y\<in>S. dist a y \<le> e)"
  unfolding bounded_def
  apply safe
  apply (rule_tac x="dist a x + e" in exI)
  apply clarify
  apply (drule (1) bspec)
  apply (erule order_trans [OF dist_triangle add_left_mono])
  apply auto
  done

lemma bounded_iff: "bounded S \<longleftrightarrow> (\<exists>a. \<forall>x\<in>S. norm x \<le> a)"
  unfolding bounded_any_center [where a=0]
  by (simp add: dist_norm)

lemma bounded_realI:
  assumes "\<forall>x\<in>s. abs (x::real) \<le> B"
  shows "bounded s"
  unfolding bounded_def dist_real_def
  apply (rule_tac x=0 in exI)
  using assms
  apply auto
  done

lemma bounded_empty [simp]: "bounded {}"
  by (simp add: bounded_def)

lemma bounded_subset: "bounded T \<Longrightarrow> S \<subseteq> T \<Longrightarrow> bounded S"
  by (metis bounded_def subset_eq)

lemma bounded_interior[intro]: "bounded S \<Longrightarrow> bounded(interior S)"
  by (metis bounded_subset interior_subset)

lemma bounded_closure[intro]:
  assumes "bounded S"
  shows "bounded (closure S)"
proof -
  from assms obtain x and a where a: "\<forall>y\<in>S. dist x y \<le> a"
    unfolding bounded_def by auto
  {
    fix y
    assume "y \<in> closure S"
    then obtain f where f: "\<forall>n. f n \<in> S"  "(f ---> y) sequentially"
      unfolding closure_sequential by auto
    have "\<forall>n. f n \<in> S \<longrightarrow> dist x (f n) \<le> a" using a by simp
    then have "eventually (\<lambda>n. dist x (f n) \<le> a) sequentially"
      by (rule eventually_mono, simp add: f(1))
    have "dist x y \<le> a"
      apply (rule Lim_dist_ubound [of sequentially f])
      apply (rule trivial_limit_sequentially)
      apply (rule f(2))
      apply fact
      done
  }
  then show ?thesis
    unfolding bounded_def by auto
qed

lemma bounded_cball[simp,intro]: "bounded (cball x e)"
  apply (simp add: bounded_def)
  apply (rule_tac x=x in exI)
  apply (rule_tac x=e in exI)
  apply auto
  done

lemma bounded_ball[simp,intro]: "bounded (ball x e)"
  by (metis ball_subset_cball bounded_cball bounded_subset)

lemma bounded_Un[simp]: "bounded (S \<union> T) \<longleftrightarrow> bounded S \<and> bounded T"
  apply (auto simp add: bounded_def)
  apply (rename_tac x y r s)
  apply (rule_tac x=x in exI)
  apply (rule_tac x="max r (dist x y + s)" in exI)
  apply (rule ballI)
  apply safe
  apply (drule (1) bspec)
  apply simp
  apply (drule (1) bspec)
  apply (rule max.coboundedI2)
  apply (erule order_trans [OF dist_triangle add_left_mono])
  done

lemma bounded_Union[intro]: "finite F \<Longrightarrow> \<forall>S\<in>F. bounded S \<Longrightarrow> bounded (\<Union>F)"
  by (induct rule: finite_induct[of F]) auto

lemma bounded_UN [intro]: "finite A \<Longrightarrow> \<forall>x\<in>A. bounded (B x) \<Longrightarrow> bounded (\<Union>x\<in>A. B x)"
  by (induct set: finite) auto

lemma bounded_insert [simp]: "bounded (insert x S) \<longleftrightarrow> bounded S"
proof -
  have "\<forall>y\<in>{x}. dist x y \<le> 0"
    by simp
  then have "bounded {x}"
    unfolding bounded_def by fast
  then show ?thesis
    by (metis insert_is_Un bounded_Un)
qed

lemma finite_imp_bounded [intro]: "finite S \<Longrightarrow> bounded S"
  by (induct set: finite) simp_all

lemma bounded_pos: "bounded S \<longleftrightarrow> (\<exists>b>0. \<forall>x\<in> S. norm x \<le> b)"
  apply (simp add: bounded_iff)
  apply (subgoal_tac "\<And>x (y::real). 0 < 1 + abs y \<and> (x \<le> y \<longrightarrow> x \<le> 1 + abs y)")
  apply metis
  apply arith
  done

lemma Bseq_eq_bounded:
  fixes f :: "nat \<Rightarrow> 'a::real_normed_vector"
  shows "Bseq f \<longleftrightarrow> bounded (range f)"
  unfolding Bseq_def bounded_pos by auto

lemma bounded_Int[intro]: "bounded S \<or> bounded T \<Longrightarrow> bounded (S \<inter> T)"
  by (metis Int_lower1 Int_lower2 bounded_subset)

lemma bounded_diff[intro]: "bounded S \<Longrightarrow> bounded (S - T)"
  by (metis Diff_subset bounded_subset)

lemma not_bounded_UNIV[simp, intro]:
  "\<not> bounded (UNIV :: 'a::{real_normed_vector, perfect_space} set)"
proof (auto simp add: bounded_pos not_le)
  obtain x :: 'a where "x \<noteq> 0"
    using perfect_choose_dist [OF zero_less_one] by fast
  fix b :: real
  assume b: "b >0"
  have b1: "b +1 \<ge> 0"
    using b by simp
  with `x \<noteq> 0` have "b < norm (scaleR (b + 1) (sgn x))"
    by (simp add: norm_sgn)
  then show "\<exists>x::'a. b < norm x" ..
qed

lemma bounded_linear_image:
  assumes "bounded S"
    and "bounded_linear f"
  shows "bounded (f ` S)"
proof -
  from assms(1) obtain b where b: "b > 0" "\<forall>x\<in>S. norm x \<le> b"
    unfolding bounded_pos by auto
  from assms(2) obtain B where B: "B > 0" "\<forall>x. norm (f x) \<le> B * norm x"
    using bounded_linear.pos_bounded by (auto simp add: mult_ac)
  {
    fix x
    assume "x \<in> S"
    then have "norm x \<le> b"
      using b by auto
    then have "norm (f x) \<le> B * b"
      using B(2)
      apply (erule_tac x=x in allE)
      apply (metis B(1) B(2) order_trans mult_le_cancel_left_pos)
      done
  }
  then show ?thesis
    unfolding bounded_pos
    apply (rule_tac x="b*B" in exI)
    using b B mult_pos_pos [of b B]
    apply (auto simp add: mult_commute)
    done
qed

lemma bounded_scaling:
  fixes S :: "'a::real_normed_vector set"
  shows "bounded S \<Longrightarrow> bounded ((\<lambda>x. c *\<^sub>R x) ` S)"
  apply (rule bounded_linear_image)
  apply assumption
  apply (rule bounded_linear_scaleR_right)
  done

lemma bounded_translation:
  fixes S :: "'a::real_normed_vector set"
  assumes "bounded S"
  shows "bounded ((\<lambda>x. a + x) ` S)"
proof -
  from assms obtain b where b: "b > 0" "\<forall>x\<in>S. norm x \<le> b"
    unfolding bounded_pos by auto
  {
    fix x
    assume "x \<in> S"
    then have "norm (a + x) \<le> b + norm a"
      using norm_triangle_ineq[of a x] b by auto
  }
  then show ?thesis
    unfolding bounded_pos
    using norm_ge_zero[of a] b(1) and add_strict_increasing[of b 0 "norm a"]
    by (auto intro!: exI[of _ "b + norm a"])
qed


text{* Some theorems on sups and infs using the notion "bounded". *}

lemma bounded_real: "bounded (S::real set) \<longleftrightarrow> (\<exists>a. \<forall>x\<in>S. \<bar>x\<bar> \<le> a)"
  by (simp add: bounded_iff)

lemma bounded_imp_bdd_above: "bounded S \<Longrightarrow> bdd_above (S :: real set)"
  by (auto simp: bounded_def bdd_above_def dist_real_def)
     (metis abs_le_D1 abs_minus_commute diff_le_eq)

lemma bounded_imp_bdd_below: "bounded S \<Longrightarrow> bdd_below (S :: real set)"
  by (auto simp: bounded_def bdd_below_def dist_real_def)
     (metis abs_le_D1 add_commute diff_le_eq)

(* TODO: remove the following lemmas about Inf and Sup, is now in conditionally complete lattice *)

lemma bounded_has_Sup:
  fixes S :: "real set"
  assumes "bounded S"
    and "S \<noteq> {}"
  shows "\<forall>x\<in>S. x \<le> Sup S"
    and "\<forall>b. (\<forall>x\<in>S. x \<le> b) \<longrightarrow> Sup S \<le> b"
proof
  show "\<forall>b. (\<forall>x\<in>S. x \<le> b) \<longrightarrow> Sup S \<le> b"
    using assms by (metis cSup_least)
qed (metis cSup_upper assms(1) bounded_imp_bdd_above)

lemma Sup_insert:
  fixes S :: "real set"
  shows "bounded S \<Longrightarrow> Sup (insert x S) = (if S = {} then x else max x (Sup S))"
  by (auto simp: bounded_imp_bdd_above sup_max cSup_insert_If)

lemma Sup_insert_finite:
  fixes S :: "real set"
  shows "finite S \<Longrightarrow> Sup (insert x S) = (if S = {} then x else max x (Sup S))"
  apply (rule Sup_insert)
  apply (rule finite_imp_bounded)
  apply simp
  done

lemma bounded_has_Inf:
  fixes S :: "real set"
  assumes "bounded S"
    and "S \<noteq> {}"
  shows "\<forall>x\<in>S. x \<ge> Inf S"
    and "\<forall>b. (\<forall>x\<in>S. x \<ge> b) \<longrightarrow> Inf S \<ge> b"
proof
  show "\<forall>b. (\<forall>x\<in>S. x \<ge> b) \<longrightarrow> Inf S \<ge> b"
    using assms by (metis cInf_greatest)
qed (metis cInf_lower assms(1) bounded_imp_bdd_below)

lemma Inf_insert:
  fixes S :: "real set"
  shows "bounded S \<Longrightarrow> Inf (insert x S) = (if S = {} then x else min x (Inf S))"
  by (auto simp: bounded_imp_bdd_below inf_min cInf_insert_If)

lemma Inf_insert_finite:
  fixes S :: "real set"
  shows "finite S \<Longrightarrow> Inf (insert x S) = (if S = {} then x else min x (Inf S))"
  apply (rule Inf_insert)
  apply (rule finite_imp_bounded)
  apply simp
  done

subsection {* Compactness *}

subsubsection {* Bolzano-Weierstrass property *}

lemma heine_borel_imp_bolzano_weierstrass:
  assumes "compact s"
    and "infinite t"
    and "t \<subseteq> s"
  shows "\<exists>x \<in> s. x islimpt t"
proof (rule ccontr)
  assume "\<not> (\<exists>x \<in> s. x islimpt t)"
  then obtain f where f: "\<forall>x\<in>s. x \<in> f x \<and> open (f x) \<and> (\<forall>y\<in>t. y \<in> f x \<longrightarrow> y = x)"
    unfolding islimpt_def
    using bchoice[of s "\<lambda> x T. x \<in> T \<and> open T \<and> (\<forall>y\<in>t. y \<in> T \<longrightarrow> y = x)"]
    by auto
  obtain g where g: "g \<subseteq> {t. \<exists>x. x \<in> s \<and> t = f x}" "finite g" "s \<subseteq> \<Union>g"
    using assms(1)[unfolded compact_eq_heine_borel, THEN spec[where x="{t. \<exists>x. x\<in>s \<and> t = f x}"]]
    using f by auto
  from g(1,3) have g':"\<forall>x\<in>g. \<exists>xa \<in> s. x = f xa"
    by auto
  {
    fix x y
    assume "x \<in> t" "y \<in> t" "f x = f y"
    then have "x \<in> f x"  "y \<in> f x \<longrightarrow> y = x"
      using f[THEN bspec[where x=x]] and `t \<subseteq> s` by auto
    then have "x = y"
      using `f x = f y` and f[THEN bspec[where x=y]] and `y \<in> t` and `t \<subseteq> s`
      by auto
  }
  then have "inj_on f t"
    unfolding inj_on_def by simp
  then have "infinite (f ` t)"
    using assms(2) using finite_imageD by auto
  moreover
  {
    fix x
    assume "x \<in> t" "f x \<notin> g"
    from g(3) assms(3) `x \<in> t` obtain h where "h \<in> g" and "x \<in> h"
      by auto
    then obtain y where "y \<in> s" "h = f y"
      using g'[THEN bspec[where x=h]] by auto
    then have "y = x"
      using f[THEN bspec[where x=y]] and `x\<in>t` and `x\<in>h`[unfolded `h = f y`]
      by auto
    then have False
      using `f x \<notin> g` `h \<in> g` unfolding `h = f y`
      by auto
  }
  then have "f ` t \<subseteq> g" by auto
  ultimately show False
    using g(2) using finite_subset by auto
qed

lemma acc_point_range_imp_convergent_subsequence:
  fixes l :: "'a :: first_countable_topology"
  assumes l: "\<forall>U. l\<in>U \<longrightarrow> open U \<longrightarrow> infinite (U \<inter> range f)"
  shows "\<exists>r. subseq r \<and> (f \<circ> r) ----> l"
proof -
  from countable_basis_at_decseq[of l]
  obtain A where A:
      "\<And>i. open (A i)"
      "\<And>i. l \<in> A i"
      "\<And>S. open S \<Longrightarrow> l \<in> S \<Longrightarrow> eventually (\<lambda>i. A i \<subseteq> S) sequentially"
    by blast
  def s \<equiv> "\<lambda>n i. SOME j. i < j \<and> f j \<in> A (Suc n)"
  {
    fix n i
    have "infinite (A (Suc n) \<inter> range f - f`{.. i})"
      using l A by auto
    then have "\<exists>x. x \<in> A (Suc n) \<inter> range f - f`{.. i}"
      unfolding ex_in_conv by (intro notI) simp
    then have "\<exists>j. f j \<in> A (Suc n) \<and> j \<notin> {.. i}"
      by auto
    then have "\<exists>a. i < a \<and> f a \<in> A (Suc n)"
      by (auto simp: not_le)
    then have "i < s n i" "f (s n i) \<in> A (Suc n)"
      unfolding s_def by (auto intro: someI2_ex)
  }
  note s = this
  def r \<equiv> "rec_nat (s 0 0) s"
  have "subseq r"
    by (auto simp: r_def s subseq_Suc_iff)
  moreover
  have "(\<lambda>n. f (r n)) ----> l"
  proof (rule topological_tendstoI)
    fix S
    assume "open S" "l \<in> S"
    with A(3) have "eventually (\<lambda>i. A i \<subseteq> S) sequentially"
      by auto
    moreover
    {
      fix i
      assume "Suc 0 \<le> i"
      then have "f (r i) \<in> A i"
        by (cases i) (simp_all add: r_def s)
    }
    then have "eventually (\<lambda>i. f (r i) \<in> A i) sequentially"
      by (auto simp: eventually_sequentially)
    ultimately show "eventually (\<lambda>i. f (r i) \<in> S) sequentially"
      by eventually_elim auto
  qed
  ultimately show "\<exists>r. subseq r \<and> (f \<circ> r) ----> l"
    by (auto simp: convergent_def comp_def)
qed

lemma sequence_infinite_lemma:
  fixes f :: "nat \<Rightarrow> 'a::t1_space"
  assumes "\<forall>n. f n \<noteq> l"
    and "(f ---> l) sequentially"
  shows "infinite (range f)"
proof
  assume "finite (range f)"
  then have "closed (range f)"
    by (rule finite_imp_closed)
  then have "open (- range f)"
    by (rule open_Compl)
  from assms(1) have "l \<in> - range f"
    by auto
  from assms(2) have "eventually (\<lambda>n. f n \<in> - range f) sequentially"
    using `open (- range f)` `l \<in> - range f`
    by (rule topological_tendstoD)
  then show False
    unfolding eventually_sequentially
    by auto
qed

lemma closure_insert:
  fixes x :: "'a::t1_space"
  shows "closure (insert x s) = insert x (closure s)"
  apply (rule closure_unique)
  apply (rule insert_mono [OF closure_subset])
  apply (rule closed_insert [OF closed_closure])
  apply (simp add: closure_minimal)
  done

lemma islimpt_insert:
  fixes x :: "'a::t1_space"
  shows "x islimpt (insert a s) \<longleftrightarrow> x islimpt s"
proof
  assume *: "x islimpt (insert a s)"
  show "x islimpt s"
  proof (rule islimptI)
    fix t
    assume t: "x \<in> t" "open t"
    show "\<exists>y\<in>s. y \<in> t \<and> y \<noteq> x"
    proof (cases "x = a")
      case True
      obtain y where "y \<in> insert a s" "y \<in> t" "y \<noteq> x"
        using * t by (rule islimptE)
      with `x = a` show ?thesis by auto
    next
      case False
      with t have t': "x \<in> t - {a}" "open (t - {a})"
        by (simp_all add: open_Diff)
      obtain y where "y \<in> insert a s" "y \<in> t - {a}" "y \<noteq> x"
        using * t' by (rule islimptE)
      then show ?thesis by auto
    qed
  qed
next
  assume "x islimpt s"
  then show "x islimpt (insert a s)"
    by (rule islimpt_subset) auto
qed

lemma islimpt_finite:
  fixes x :: "'a::t1_space"
  shows "finite s \<Longrightarrow> \<not> x islimpt s"
  by (induct set: finite) (simp_all add: islimpt_insert)

lemma islimpt_union_finite:
  fixes x :: "'a::t1_space"
  shows "finite s \<Longrightarrow> x islimpt (s \<union> t) \<longleftrightarrow> x islimpt t"
  by (simp add: islimpt_Un islimpt_finite)

lemma islimpt_eq_acc_point:
  fixes l :: "'a :: t1_space"
  shows "l islimpt S \<longleftrightarrow> (\<forall>U. l\<in>U \<longrightarrow> open U \<longrightarrow> infinite (U \<inter> S))"
proof (safe intro!: islimptI)
  fix U
  assume "l islimpt S" "l \<in> U" "open U" "finite (U \<inter> S)"
  then have "l islimpt S" "l \<in> (U - (U \<inter> S - {l}))" "open (U - (U \<inter> S - {l}))"
    by (auto intro: finite_imp_closed)
  then show False
    by (rule islimptE) auto
next
  fix T
  assume *: "\<forall>U. l\<in>U \<longrightarrow> open U \<longrightarrow> infinite (U \<inter> S)" "l \<in> T" "open T"
  then have "infinite (T \<inter> S - {l})"
    by auto
  then have "\<exists>x. x \<in> (T \<inter> S - {l})"
    unfolding ex_in_conv by (intro notI) simp
  then show "\<exists>y\<in>S. y \<in> T \<and> y \<noteq> l"
    by auto
qed

lemma islimpt_range_imp_convergent_subsequence:
  fixes l :: "'a :: {t1_space, first_countable_topology}"
  assumes l: "l islimpt (range f)"
  shows "\<exists>r. subseq r \<and> (f \<circ> r) ----> l"
  using l unfolding islimpt_eq_acc_point
  by (rule acc_point_range_imp_convergent_subsequence)

lemma sequence_unique_limpt:
  fixes f :: "nat \<Rightarrow> 'a::t2_space"
  assumes "(f ---> l) sequentially"
    and "l' islimpt (range f)"
  shows "l' = l"
proof (rule ccontr)
  assume "l' \<noteq> l"
  obtain s t where "open s" "open t" "l' \<in> s" "l \<in> t" "s \<inter> t = {}"
    using hausdorff [OF `l' \<noteq> l`] by auto
  have "eventually (\<lambda>n. f n \<in> t) sequentially"
    using assms(1) `open t` `l \<in> t` by (rule topological_tendstoD)
  then obtain N where "\<forall>n\<ge>N. f n \<in> t"
    unfolding eventually_sequentially by auto

  have "UNIV = {..<N} \<union> {N..}"
    by auto
  then have "l' islimpt (f ` ({..<N} \<union> {N..}))"
    using assms(2) by simp
  then have "l' islimpt (f ` {..<N} \<union> f ` {N..})"
    by (simp add: image_Un)
  then have "l' islimpt (f ` {N..})"
    by (simp add: islimpt_union_finite)
  then obtain y where "y \<in> f ` {N..}" "y \<in> s" "y \<noteq> l'"
    using `l' \<in> s` `open s` by (rule islimptE)
  then obtain n where "N \<le> n" "f n \<in> s" "f n \<noteq> l'"
    by auto
  with `\<forall>n\<ge>N. f n \<in> t` have "f n \<in> s \<inter> t"
    by simp
  with `s \<inter> t = {}` show False
    by simp
qed

lemma bolzano_weierstrass_imp_closed:
  fixes s :: "'a::{first_countable_topology,t2_space} set"
  assumes "\<forall>t. infinite t \<and> t \<subseteq> s --> (\<exists>x \<in> s. x islimpt t)"
  shows "closed s"
proof -
  {
    fix x l
    assume as: "\<forall>n::nat. x n \<in> s" "(x ---> l) sequentially"
    then have "l \<in> s"
    proof (cases "\<forall>n. x n \<noteq> l")
      case False
      then show "l\<in>s" using as(1) by auto
    next
      case True note cas = this
      with as(2) have "infinite (range x)"
        using sequence_infinite_lemma[of x l] by auto
      then obtain l' where "l'\<in>s" "l' islimpt (range x)"
        using assms[THEN spec[where x="range x"]] as(1) by auto
      then show "l\<in>s" using sequence_unique_limpt[of x l l']
        using as cas by auto
    qed
  }
  then show ?thesis
    unfolding closed_sequential_limits by fast
qed

lemma compact_imp_bounded:
  assumes "compact U"
  shows "bounded U"
proof -
  have "compact U" "\<forall>x\<in>U. open (ball x 1)" "U \<subseteq> (\<Union>x\<in>U. ball x 1)"
    using assms by auto
  then obtain D where D: "D \<subseteq> U" "finite D" "U \<subseteq> (\<Union>x\<in>D. ball x 1)"
    by (rule compactE_image)
  from `finite D` have "bounded (\<Union>x\<in>D. ball x 1)"
    by (simp add: bounded_UN)
  then show "bounded U" using `U \<subseteq> (\<Union>x\<in>D. ball x 1)`
    by (rule bounded_subset)
qed

text{* In particular, some common special cases. *}

lemma compact_union [intro]:
  assumes "compact s"
    and "compact t"
  shows " compact (s \<union> t)"
proof (rule compactI)
  fix f
  assume *: "Ball f open" "s \<union> t \<subseteq> \<Union>f"
  from * `compact s` obtain s' where "s' \<subseteq> f \<and> finite s' \<and> s \<subseteq> \<Union>s'"
    unfolding compact_eq_heine_borel by (auto elim!: allE[of _ f]) metis
  moreover
  from * `compact t` obtain t' where "t' \<subseteq> f \<and> finite t' \<and> t \<subseteq> \<Union>t'"
    unfolding compact_eq_heine_borel by (auto elim!: allE[of _ f]) metis
  ultimately show "\<exists>f'\<subseteq>f. finite f' \<and> s \<union> t \<subseteq> \<Union>f'"
    by (auto intro!: exI[of _ "s' \<union> t'"])
qed

lemma compact_Union [intro]: "finite S \<Longrightarrow> (\<And>T. T \<in> S \<Longrightarrow> compact T) \<Longrightarrow> compact (\<Union>S)"
  by (induct set: finite) auto

lemma compact_UN [intro]:
  "finite A \<Longrightarrow> (\<And>x. x \<in> A \<Longrightarrow> compact (B x)) \<Longrightarrow> compact (\<Union>x\<in>A. B x)"
  unfolding SUP_def by (rule compact_Union) auto

lemma closed_inter_compact [intro]:
  assumes "closed s"
    and "compact t"
  shows "compact (s \<inter> t)"
  using compact_inter_closed [of t s] assms
  by (simp add: Int_commute)

lemma compact_inter [intro]:
  fixes s t :: "'a :: t2_space set"
  assumes "compact s"
    and "compact t"
  shows "compact (s \<inter> t)"
  using assms by (intro compact_inter_closed compact_imp_closed)

lemma compact_sing [simp]: "compact {a}"
  unfolding compact_eq_heine_borel by auto

lemma compact_insert [simp]:
  assumes "compact s"
  shows "compact (insert x s)"
proof -
  have "compact ({x} \<union> s)"
    using compact_sing assms by (rule compact_union)
  then show ?thesis by simp
qed

lemma finite_imp_compact: "finite s \<Longrightarrow> compact s"
  by (induct set: finite) simp_all

lemma open_delete:
  fixes s :: "'a::t1_space set"
  shows "open s \<Longrightarrow> open (s - {x})"
  by (simp add: open_Diff)

text{*Compactness expressed with filters*}

definition "filter_from_subbase B = Abs_filter (\<lambda>P. \<exists>X \<subseteq> B. finite X \<and> Inf X \<le> P)"

lemma eventually_filter_from_subbase:
  "eventually P (filter_from_subbase B) \<longleftrightarrow> (\<exists>X \<subseteq> B. finite X \<and> Inf X \<le> P)"
    (is "_ \<longleftrightarrow> ?R P")
  unfolding filter_from_subbase_def
proof (rule eventually_Abs_filter is_filter.intro)+
  show "?R (\<lambda>x. True)"
    by (rule exI[of _ "{}"]) (simp add: le_fun_def)
next
  fix P Q
  assume "?R P" then guess X ..
  moreover
  assume "?R Q" then guess Y ..
  ultimately show "?R (\<lambda>x. P x \<and> Q x)"
    by (intro exI[of _ "X \<union> Y"]) auto
next
  fix P Q
  assume "?R P" then guess X ..
  moreover assume "\<forall>x. P x \<longrightarrow> Q x"
  ultimately show "?R Q"
    by (intro exI[of _ X]) auto
qed

lemma eventually_filter_from_subbaseI: "P \<in> B \<Longrightarrow> eventually P (filter_from_subbase B)"
  by (subst eventually_filter_from_subbase) (auto intro!: exI[of _ "{P}"])

lemma filter_from_subbase_not_bot:
  "\<forall>X \<subseteq> B. finite X \<longrightarrow> Inf X \<noteq> bot \<Longrightarrow> filter_from_subbase B \<noteq> bot"
  unfolding trivial_limit_def eventually_filter_from_subbase by auto

lemma closure_iff_nhds_not_empty:
  "x \<in> closure X \<longleftrightarrow> (\<forall>A. \<forall>S\<subseteq>A. open S \<longrightarrow> x \<in> S \<longrightarrow> X \<inter> A \<noteq> {})"
proof safe
  assume x: "x \<in> closure X"
  fix S A
  assume "open S" "x \<in> S" "X \<inter> A = {}" "S \<subseteq> A"
  then have "x \<notin> closure (-S)"
    by (auto simp: closure_complement subset_eq[symmetric] intro: interiorI)
  with x have "x \<in> closure X - closure (-S)"
    by auto
  also have "\<dots> \<subseteq> closure (X \<inter> S)"
    using `open S` open_inter_closure_subset[of S X] by (simp add: closed_Compl ac_simps)
  finally have "X \<inter> S \<noteq> {}" by auto
  then show False using `X \<inter> A = {}` `S \<subseteq> A` by auto
next
  assume "\<forall>A S. S \<subseteq> A \<longrightarrow> open S \<longrightarrow> x \<in> S \<longrightarrow> X \<inter> A \<noteq> {}"
  from this[THEN spec, of "- X", THEN spec, of "- closure X"]
  show "x \<in> closure X"
    by (simp add: closure_subset open_Compl)
qed

lemma compact_filter:
  "compact U \<longleftrightarrow> (\<forall>F. F \<noteq> bot \<longrightarrow> eventually (\<lambda>x. x \<in> U) F \<longrightarrow> (\<exists>x\<in>U. inf (nhds x) F \<noteq> bot))"
proof (intro allI iffI impI compact_fip[THEN iffD2] notI)
  fix F
  assume "compact U"
  assume F: "F \<noteq> bot" "eventually (\<lambda>x. x \<in> U) F"
  then have "U \<noteq> {}"
    by (auto simp: eventually_False)

  def Z \<equiv> "closure ` {A. eventually (\<lambda>x. x \<in> A) F}"
  then have "\<forall>z\<in>Z. closed z"
    by auto
  moreover
  have ev_Z: "\<And>z. z \<in> Z \<Longrightarrow> eventually (\<lambda>x. x \<in> z) F"
    unfolding Z_def by (auto elim: eventually_elim1 intro: set_mp[OF closure_subset])
  have "(\<forall>B \<subseteq> Z. finite B \<longrightarrow> U \<inter> \<Inter>B \<noteq> {})"
  proof (intro allI impI)
    fix B assume "finite B" "B \<subseteq> Z"
    with `finite B` ev_Z have "eventually (\<lambda>x. \<forall>b\<in>B. x \<in> b) F"
      by (auto intro!: eventually_Ball_finite)
    with F(2) have "eventually (\<lambda>x. x \<in> U \<inter> (\<Inter>B)) F"
      by eventually_elim auto
    with F show "U \<inter> \<Inter>B \<noteq> {}"
      by (intro notI) (simp add: eventually_False)
  qed
  ultimately have "U \<inter> \<Inter>Z \<noteq> {}"
    using `compact U` unfolding compact_fip by blast
  then obtain x where "x \<in> U" and x: "\<And>z. z \<in> Z \<Longrightarrow> x \<in> z"
    by auto

  have "\<And>P. eventually P (inf (nhds x) F) \<Longrightarrow> P \<noteq> bot"
    unfolding eventually_inf eventually_nhds
  proof safe
    fix P Q R S
    assume "eventually R F" "open S" "x \<in> S"
    with open_inter_closure_eq_empty[of S "{x. R x}"] x[of "closure {x. R x}"]
    have "S \<inter> {x. R x} \<noteq> {}" by (auto simp: Z_def)
    moreover assume "Ball S Q" "\<forall>x. Q x \<and> R x \<longrightarrow> bot x"
    ultimately show False by (auto simp: set_eq_iff)
  qed
  with `x \<in> U` show "\<exists>x\<in>U. inf (nhds x) F \<noteq> bot"
    by (metis eventually_bot)
next
  fix A
  assume A: "\<forall>a\<in>A. closed a" "\<forall>B\<subseteq>A. finite B \<longrightarrow> U \<inter> \<Inter>B \<noteq> {}" "U \<inter> \<Inter>A = {}"
  def P' \<equiv> "(\<lambda>a (x::'a). x \<in> a)"
  then have inj_P': "\<And>A. inj_on P' A"
    by (auto intro!: inj_onI simp: fun_eq_iff)
  def F \<equiv> "filter_from_subbase (P' ` insert U A)"
  have "F \<noteq> bot"
    unfolding F_def
  proof (safe intro!: filter_from_subbase_not_bot)
    fix X
    assume "X \<subseteq> P' ` insert U A" "finite X" "Inf X = bot"
    then obtain B where "B \<subseteq> insert U A" "finite B" and B: "Inf (P' ` B) = bot"
      unfolding subset_image_iff by (auto intro: inj_P' finite_imageD)
    with A(2)[THEN spec, of "B - {U}"] have "U \<inter> \<Inter>(B - {U}) \<noteq> {}"
      by auto
    with B show False
      by (auto simp: P'_def fun_eq_iff)
  qed
  moreover have "eventually (\<lambda>x. x \<in> U) F"
    unfolding F_def by (rule eventually_filter_from_subbaseI) (auto simp: P'_def)
  moreover
  assume "\<forall>F. F \<noteq> bot \<longrightarrow> eventually (\<lambda>x. x \<in> U) F \<longrightarrow> (\<exists>x\<in>U. inf (nhds x) F \<noteq> bot)"
  ultimately obtain x where "x \<in> U" and x: "inf (nhds x) F \<noteq> bot"
    by auto

  {
    fix V
    assume "V \<in> A"
    then have V: "eventually (\<lambda>x. x \<in> V) F"
      by (auto simp add: F_def image_iff P'_def intro!: eventually_filter_from_subbaseI)
    have "x \<in> closure V"
      unfolding closure_iff_nhds_not_empty
    proof (intro impI allI)
      fix S A
      assume "open S" "x \<in> S" "S \<subseteq> A"
      then have "eventually (\<lambda>x. x \<in> A) (nhds x)"
        by (auto simp: eventually_nhds)
      with V have "eventually (\<lambda>x. x \<in> V \<inter> A) (inf (nhds x) F)"
        by (auto simp: eventually_inf)
      with x show "V \<inter> A \<noteq> {}"
        by (auto simp del: Int_iff simp add: trivial_limit_def)
    qed
    then have "x \<in> V"
      using `V \<in> A` A(1) by simp
  }
  with `x\<in>U` have "x \<in> U \<inter> \<Inter>A" by auto
  with `U \<inter> \<Inter>A = {}` show False by auto
qed

definition "countably_compact U \<longleftrightarrow>
    (\<forall>A. countable A \<longrightarrow> (\<forall>a\<in>A. open a) \<longrightarrow> U \<subseteq> \<Union>A \<longrightarrow> (\<exists>T\<subseteq>A. finite T \<and> U \<subseteq> \<Union>T))"

lemma countably_compactE:
  assumes "countably_compact s" and "\<forall>t\<in>C. open t" and "s \<subseteq> \<Union>C" "countable C"
  obtains C' where "C' \<subseteq> C" and "finite C'" and "s \<subseteq> \<Union>C'"
  using assms unfolding countably_compact_def by metis

lemma countably_compactI:
  assumes "\<And>C. \<forall>t\<in>C. open t \<Longrightarrow> s \<subseteq> \<Union>C \<Longrightarrow> countable C \<Longrightarrow> (\<exists>C'\<subseteq>C. finite C' \<and> s \<subseteq> \<Union>C')"
  shows "countably_compact s"
  using assms unfolding countably_compact_def by metis

lemma compact_imp_countably_compact: "compact U \<Longrightarrow> countably_compact U"
  by (auto simp: compact_eq_heine_borel countably_compact_def)

lemma countably_compact_imp_compact:
  assumes "countably_compact U"
    and ccover: "countable B" "\<forall>b\<in>B. open b"
    and basis: "\<And>T x. open T \<Longrightarrow> x \<in> T \<Longrightarrow> x \<in> U \<Longrightarrow> \<exists>b\<in>B. x \<in> b \<and> b \<inter> U \<subseteq> T"
  shows "compact U"
  using `countably_compact U`
  unfolding compact_eq_heine_borel countably_compact_def
proof safe
  fix A
  assume A: "\<forall>a\<in>A. open a" "U \<subseteq> \<Union>A"
  assume *: "\<forall>A. countable A \<longrightarrow> (\<forall>a\<in>A. open a) \<longrightarrow> U \<subseteq> \<Union>A \<longrightarrow> (\<exists>T\<subseteq>A. finite T \<and> U \<subseteq> \<Union>T)"

  moreover def C \<equiv> "{b\<in>B. \<exists>a\<in>A. b \<inter> U \<subseteq> a}"
  ultimately have "countable C" "\<forall>a\<in>C. open a"
    unfolding C_def using ccover by auto
  moreover
  have "\<Union>A \<inter> U \<subseteq> \<Union>C"
  proof safe
    fix x a
    assume "x \<in> U" "x \<in> a" "a \<in> A"
    with basis[of a x] A obtain b where "b \<in> B" "x \<in> b" "b \<inter> U \<subseteq> a"
      by blast
    with `a \<in> A` show "x \<in> \<Union>C"
      unfolding C_def by auto
  qed
  then have "U \<subseteq> \<Union>C" using `U \<subseteq> \<Union>A` by auto
  ultimately obtain T where T: "T\<subseteq>C" "finite T" "U \<subseteq> \<Union>T"
    using * by metis
  then have "\<forall>t\<in>T. \<exists>a\<in>A. t \<inter> U \<subseteq> a"
    by (auto simp: C_def)
  then obtain f where "\<forall>t\<in>T. f t \<in> A \<and> t \<inter> U \<subseteq> f t"
    unfolding bchoice_iff Bex_def ..
  with T show "\<exists>T\<subseteq>A. finite T \<and> U \<subseteq> \<Union>T"
    unfolding C_def by (intro exI[of _ "f`T"]) fastforce
qed

lemma countably_compact_imp_compact_second_countable:
  "countably_compact U \<Longrightarrow> compact (U :: 'a :: second_countable_topology set)"
proof (rule countably_compact_imp_compact)
  fix T and x :: 'a
  assume "open T" "x \<in> T"
  from topological_basisE[OF is_basis this] obtain b where
    "b \<in> (SOME B. countable B \<and> topological_basis B)" "x \<in> b" "b \<subseteq> T" .
  then show "\<exists>b\<in>SOME B. countable B \<and> topological_basis B. x \<in> b \<and> b \<inter> U \<subseteq> T"
    by blast
qed (insert countable_basis topological_basis_open[OF is_basis], auto)

lemma countably_compact_eq_compact:
  "countably_compact U \<longleftrightarrow> compact (U :: 'a :: second_countable_topology set)"
  using countably_compact_imp_compact_second_countable compact_imp_countably_compact by blast

subsubsection{* Sequential compactness *}

definition seq_compact :: "'a::topological_space set \<Rightarrow> bool"
  where "seq_compact S \<longleftrightarrow>
    (\<forall>f. (\<forall>n. f n \<in> S) \<longrightarrow> (\<exists>l\<in>S. \<exists>r. subseq r \<and> ((f \<circ> r) ---> l) sequentially))"

lemma seq_compactI:
  assumes "\<And>f. \<forall>n. f n \<in> S \<Longrightarrow> \<exists>l\<in>S. \<exists>r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"
  shows "seq_compact S"
  unfolding seq_compact_def using assms by fast

lemma seq_compactE:
  assumes "seq_compact S" "\<forall>n. f n \<in> S"
  obtains l r where "l \<in> S" "subseq r" "((f \<circ> r) ---> l) sequentially"
  using assms unfolding seq_compact_def by fast

lemma closed_sequentially: (* TODO: move upwards *)
  assumes "closed s" and "\<forall>n. f n \<in> s" and "f ----> l"
  shows "l \<in> s"
proof (rule ccontr)
  assume "l \<notin> s"
  with `closed s` and `f ----> l` have "eventually (\<lambda>n. f n \<in> - s) sequentially"
    by (fast intro: topological_tendstoD)
  with `\<forall>n. f n \<in> s` show "False"
    by simp
qed

lemma seq_compact_inter_closed:
  assumes "seq_compact s" and "closed t"
  shows "seq_compact (s \<inter> t)"
proof (rule seq_compactI)
  fix f assume "\<forall>n::nat. f n \<in> s \<inter> t"
  hence "\<forall>n. f n \<in> s" and "\<forall>n. f n \<in> t"
    by simp_all
  from `seq_compact s` and `\<forall>n. f n \<in> s`
  obtain l r where "l \<in> s" and r: "subseq r" and l: "(f \<circ> r) ----> l"
    by (rule seq_compactE)
  from `\<forall>n. f n \<in> t` have "\<forall>n. (f \<circ> r) n \<in> t"
    by simp
  from `closed t` and this and l have "l \<in> t"
    by (rule closed_sequentially)
  with `l \<in> s` and r and l show "\<exists>l\<in>s \<inter> t. \<exists>r. subseq r \<and> (f \<circ> r) ----> l"
    by fast
qed

lemma seq_compact_closed_subset:
  assumes "closed s" and "s \<subseteq> t" and "seq_compact t"
  shows "seq_compact s"
  using assms seq_compact_inter_closed [of t s] by (simp add: Int_absorb1)

lemma seq_compact_imp_countably_compact:
  fixes U :: "'a :: first_countable_topology set"
  assumes "seq_compact U"
  shows "countably_compact U"
proof (safe intro!: countably_compactI)
  fix A
  assume A: "\<forall>a\<in>A. open a" "U \<subseteq> \<Union>A" "countable A"
  have subseq: "\<And>X. range X \<subseteq> U \<Longrightarrow> \<exists>r x. x \<in> U \<and> subseq r \<and> (X \<circ> r) ----> x"
    using `seq_compact U` by (fastforce simp: seq_compact_def subset_eq)
  show "\<exists>T\<subseteq>A. finite T \<and> U \<subseteq> \<Union>T"
  proof cases
    assume "finite A"
    with A show ?thesis by auto
  next
    assume "infinite A"
    then have "A \<noteq> {}" by auto
    show ?thesis
    proof (rule ccontr)
      assume "\<not> (\<exists>T\<subseteq>A. finite T \<and> U \<subseteq> \<Union>T)"
      then have "\<forall>T. \<exists>x. T \<subseteq> A \<and> finite T \<longrightarrow> (x \<in> U - \<Union>T)"
        by auto
      then obtain X' where T: "\<And>T. T \<subseteq> A \<Longrightarrow> finite T \<Longrightarrow> X' T \<in> U - \<Union>T"
        by metis
      def X \<equiv> "\<lambda>n. X' (from_nat_into A ` {.. n})"
      have X: "\<And>n. X n \<in> U - (\<Union>i\<le>n. from_nat_into A i)"
        using `A \<noteq> {}` unfolding X_def SUP_def by (intro T) (auto intro: from_nat_into)
      then have "range X \<subseteq> U"
        by auto
      with subseq[of X] obtain r x where "x \<in> U" and r: "subseq r" "(X \<circ> r) ----> x"
        by auto
      from `x\<in>U` `U \<subseteq> \<Union>A` from_nat_into_surj[OF `countable A`]
      obtain n where "x \<in> from_nat_into A n" by auto
      with r(2) A(1) from_nat_into[OF `A \<noteq> {}`, of n]
      have "eventually (\<lambda>i. X (r i) \<in> from_nat_into A n) sequentially"
        unfolding tendsto_def by (auto simp: comp_def)
      then obtain N where "\<And>i. N \<le> i \<Longrightarrow> X (r i) \<in> from_nat_into A n"
        by (auto simp: eventually_sequentially)
      moreover from X have "\<And>i. n \<le> r i \<Longrightarrow> X (r i) \<notin> from_nat_into A n"
        by auto
      moreover from `subseq r`[THEN seq_suble, of "max n N"] have "\<exists>i. n \<le> r i \<and> N \<le> i"
        by (auto intro!: exI[of _ "max n N"])
      ultimately show False
        by auto
    qed
  qed
qed

lemma compact_imp_seq_compact:
  fixes U :: "'a :: first_countable_topology set"
  assumes "compact U"
  shows "seq_compact U"
  unfolding seq_compact_def
proof safe
  fix X :: "nat \<Rightarrow> 'a"
  assume "\<forall>n. X n \<in> U"
  then have "eventually (\<lambda>x. x \<in> U) (filtermap X sequentially)"
    by (auto simp: eventually_filtermap)
  moreover
  have "filtermap X sequentially \<noteq> bot"
    by (simp add: trivial_limit_def eventually_filtermap)
  ultimately
  obtain x where "x \<in> U" and x: "inf (nhds x) (filtermap X sequentially) \<noteq> bot" (is "?F \<noteq> _")
    using `compact U` by (auto simp: compact_filter)

  from countable_basis_at_decseq[of x]
  obtain A where A:
      "\<And>i. open (A i)"
      "\<And>i. x \<in> A i"
      "\<And>S. open S \<Longrightarrow> x \<in> S \<Longrightarrow> eventually (\<lambda>i. A i \<subseteq> S) sequentially"
    by blast
  def s \<equiv> "\<lambda>n i. SOME j. i < j \<and> X j \<in> A (Suc n)"
  {
    fix n i
    have "\<exists>a. i < a \<and> X a \<in> A (Suc n)"
    proof (rule ccontr)
      assume "\<not> (\<exists>a>i. X a \<in> A (Suc n))"
      then have "\<And>a. Suc i \<le> a \<Longrightarrow> X a \<notin> A (Suc n)"
        by auto
      then have "eventually (\<lambda>x. x \<notin> A (Suc n)) (filtermap X sequentially)"
        by (auto simp: eventually_filtermap eventually_sequentially)
      moreover have "eventually (\<lambda>x. x \<in> A (Suc n)) (nhds x)"
        using A(1,2)[of "Suc n"] by (auto simp: eventually_nhds)
      ultimately have "eventually (\<lambda>x. False) ?F"
        by (auto simp add: eventually_inf)
      with x show False
        by (simp add: eventually_False)
    qed
    then have "i < s n i" "X (s n i) \<in> A (Suc n)"
      unfolding s_def by (auto intro: someI2_ex)
  }
  note s = this
  def r \<equiv> "rec_nat (s 0 0) s"
  have "subseq r"
    by (auto simp: r_def s subseq_Suc_iff)
  moreover
  have "(\<lambda>n. X (r n)) ----> x"
  proof (rule topological_tendstoI)
    fix S
    assume "open S" "x \<in> S"
    with A(3) have "eventually (\<lambda>i. A i \<subseteq> S) sequentially"
      by auto
    moreover
    {
      fix i
      assume "Suc 0 \<le> i"
      then have "X (r i) \<in> A i"
        by (cases i) (simp_all add: r_def s)
    }
    then have "eventually (\<lambda>i. X (r i) \<in> A i) sequentially"
      by (auto simp: eventually_sequentially)
    ultimately show "eventually (\<lambda>i. X (r i) \<in> S) sequentially"
      by eventually_elim auto
  qed
  ultimately show "\<exists>x \<in> U. \<exists>r. subseq r \<and> (X \<circ> r) ----> x"
    using `x \<in> U` by (auto simp: convergent_def comp_def)
qed

lemma countably_compact_imp_acc_point:
  assumes "countably_compact s"
    and "countable t"
    and "infinite t"
    and "t \<subseteq> s"
  shows "\<exists>x\<in>s. \<forall>U. x\<in>U \<and> open U \<longrightarrow> infinite (U \<inter> t)"
proof (rule ccontr)
  def C \<equiv> "(\<lambda>F. interior (F \<union> (- t))) ` {F. finite F \<and> F \<subseteq> t }"
  note `countably_compact s`
  moreover have "\<forall>t\<in>C. open t"
    by (auto simp: C_def)
  moreover
  assume "\<not> (\<exists>x\<in>s. \<forall>U. x\<in>U \<and> open U \<longrightarrow> infinite (U \<inter> t))"
  then have s: "\<And>x. x \<in> s \<Longrightarrow> \<exists>U. x\<in>U \<and> open U \<and> finite (U \<inter> t)" by metis
  have "s \<subseteq> \<Union>C"
    using `t \<subseteq> s`
    unfolding C_def Union_image_eq
    apply (safe dest!: s)
    apply (rule_tac a="U \<inter> t" in UN_I)
    apply (auto intro!: interiorI simp add: finite_subset)
    done
  moreover
  from `countable t` have "countable C"
    unfolding C_def by (auto intro: countable_Collect_finite_subset)
  ultimately
  obtain D where "D \<subseteq> C" "finite D" "s \<subseteq> \<Union>D"
    by (rule countably_compactE)
  then obtain E where E: "E \<subseteq> {F. finite F \<and> F \<subseteq> t }" "finite E"
    and s: "s \<subseteq> (\<Union>F\<in>E. interior (F \<union> (- t)))"
    by (metis (lifting) Union_image_eq finite_subset_image C_def)
  from s `t \<subseteq> s` have "t \<subseteq> \<Union>E"
    using interior_subset by blast
  moreover have "finite (\<Union>E)"
    using E by auto
  ultimately show False using `infinite t`
    by (auto simp: finite_subset)
qed

lemma countable_acc_point_imp_seq_compact:
  fixes s :: "'a::first_countable_topology set"
  assumes "\<forall>t. infinite t \<and> countable t \<and> t \<subseteq> s \<longrightarrow>
    (\<exists>x\<in>s. \<forall>U. x\<in>U \<and> open U \<longrightarrow> infinite (U \<inter> t))"
  shows "seq_compact s"
proof -
  {
    fix f :: "nat \<Rightarrow> 'a"
    assume f: "\<forall>n. f n \<in> s"
    have "\<exists>l\<in>s. \<exists>r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"
    proof (cases "finite (range f)")
      case True
      obtain l where "infinite {n. f n = f l}"
        using pigeonhole_infinite[OF _ True] by auto
      then obtain r where "subseq r" and fr: "\<forall>n. f (r n) = f l"
        using infinite_enumerate by blast
      then have "subseq r \<and> (f \<circ> r) ----> f l"
        by (simp add: fr tendsto_const o_def)
      with f show "\<exists>l\<in>s. \<exists>r. subseq r \<and> (f \<circ> r) ----> l"
        by auto
    next
      case False
      with f assms have "\<exists>x\<in>s. \<forall>U. x\<in>U \<and> open U \<longrightarrow> infinite (U \<inter> range f)"
        by auto
      then obtain l where "l \<in> s" "\<forall>U. l\<in>U \<and> open U \<longrightarrow> infinite (U \<inter> range f)" ..
      from this(2) have "\<exists>r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"
        using acc_point_range_imp_convergent_subsequence[of l f] by auto
      with `l \<in> s` show "\<exists>l\<in>s. \<exists>r. subseq r \<and> ((f \<circ> r) ---> l) sequentially" ..
    qed
  }
  then show ?thesis
    unfolding seq_compact_def by auto
qed

lemma seq_compact_eq_countably_compact:
  fixes U :: "'a :: first_countable_topology set"
  shows "seq_compact U \<longleftrightarrow> countably_compact U"
  using
    countable_acc_point_imp_seq_compact
    countably_compact_imp_acc_point
    seq_compact_imp_countably_compact
  by metis

lemma seq_compact_eq_acc_point:
  fixes s :: "'a :: first_countable_topology set"
  shows "seq_compact s \<longleftrightarrow>
    (\<forall>t. infinite t \<and> countable t \<and> t \<subseteq> s --> (\<exists>x\<in>s. \<forall>U. x\<in>U \<and> open U \<longrightarrow> infinite (U \<inter> t)))"
  using
    countable_acc_point_imp_seq_compact[of s]
    countably_compact_imp_acc_point[of s]
    seq_compact_imp_countably_compact[of s]
  by metis

lemma seq_compact_eq_compact:
  fixes U :: "'a :: second_countable_topology set"
  shows "seq_compact U \<longleftrightarrow> compact U"
  using seq_compact_eq_countably_compact countably_compact_eq_compact by blast

lemma bolzano_weierstrass_imp_seq_compact:
  fixes s :: "'a::{t1_space, first_countable_topology} set"
  shows "\<forall>t. infinite t \<and> t \<subseteq> s --> (\<exists>x \<in> s. x islimpt t) \<Longrightarrow> seq_compact s"
  by (rule countable_acc_point_imp_seq_compact) (metis islimpt_eq_acc_point)

subsubsection{* Total boundedness *}

lemma cauchy_def: "Cauchy s \<longleftrightarrow> (\<forall>e>0. \<exists>N. \<forall>m n. m \<ge> N \<and> n \<ge> N --> dist(s m)(s n) < e)"
  unfolding Cauchy_def by metis

fun helper_1 :: "('a::metric_space set) \<Rightarrow> real \<Rightarrow> nat \<Rightarrow> 'a"
where
  "helper_1 s e n = (SOME y::'a. y \<in> s \<and> (\<forall>m<n. \<not> (dist (helper_1 s e m) y < e)))"
declare helper_1.simps[simp del]

lemma seq_compact_imp_totally_bounded:
  assumes "seq_compact s"
  shows "\<forall>e>0. \<exists>k. finite k \<and> k \<subseteq> s \<and> s \<subseteq> (\<Union>((\<lambda>x. ball x e) ` k))"
proof (rule, rule, rule ccontr)
  fix e::real
  assume "e > 0"
  assume assm: "\<not> (\<exists>k. finite k \<and> k \<subseteq> s \<and> s \<subseteq> \<Union>((\<lambda>x. ball x e) ` k))"
  def x \<equiv> "helper_1 s e"
  {
    fix n
    have "x n \<in> s \<and> (\<forall>m<n. \<not> dist (x m) (x n) < e)"
    proof (induct n rule: nat_less_induct)
      fix n
      def Q \<equiv> "(\<lambda>y. y \<in> s \<and> (\<forall>m<n. \<not> dist (x m) y < e))"
      assume as: "\<forall>m<n. x m \<in> s \<and> (\<forall>ma<m. \<not> dist (x ma) (x m) < e)"
      have "\<not> s \<subseteq> (\<Union>x\<in>x ` {0..<n}. ball x e)"
        using assm
        apply simp
        apply (erule_tac x="x ` {0 ..< n}" in allE)
        using as
        apply auto
        done
      then obtain z where z:"z\<in>s" "z \<notin> (\<Union>x\<in>x ` {0..<n}. ball x e)"
        unfolding subset_eq by auto
      have "Q (x n)"
        unfolding x_def and helper_1.simps[of s e n]
        apply (rule someI2[where a=z])
        unfolding x_def[symmetric] and Q_def
        using z
        apply auto
        done
      then show "x n \<in> s \<and> (\<forall>m<n. \<not> dist (x m) (x n) < e)"
        unfolding Q_def by auto
    qed
  }
  then have "\<forall>n::nat. x n \<in> s" and x:"\<forall>n. \<forall>m < n. \<not> (dist (x m) (x n) < e)"
    by blast+
  then obtain l r where "l\<in>s" and r:"subseq r" and "((x \<circ> r) ---> l) sequentially"
    using assms(1)[unfolded seq_compact_def, THEN spec[where x=x]] by auto
  from this(3) have "Cauchy (x \<circ> r)"
    using LIMSEQ_imp_Cauchy by auto
  then obtain N::nat where N:"\<forall>m n. N \<le> m \<and> N \<le> n \<longrightarrow> dist ((x \<circ> r) m) ((x \<circ> r) n) < e"
    unfolding cauchy_def using `e>0` by auto
  show False
    using N[THEN spec[where x=N], THEN spec[where x="N+1"]]
    using r[unfolded subseq_def, THEN spec[where x=N], THEN spec[where x="N+1"]]
    using x[THEN spec[where x="r (N+1)"], THEN spec[where x="r (N)"]]
    by auto
qed

subsubsection{* Heine-Borel theorem *}

lemma seq_compact_imp_heine_borel:
  fixes s :: "'a :: metric_space set"
  assumes "seq_compact s"
  shows "compact s"
proof -
  from seq_compact_imp_totally_bounded[OF `seq_compact s`]
  obtain f where f: "\<forall>e>0. finite (f e) \<and> f e \<subseteq> s \<and> s \<subseteq> \<Union>((\<lambda>x. ball x e) ` f e)"
    unfolding choice_iff' ..
  def K \<equiv> "(\<lambda>(x, r). ball x r) ` ((\<Union>e \<in> \<rat> \<inter> {0 <..}. f e) \<times> \<rat>)"
  have "countably_compact s"
    using `seq_compact s` by (rule seq_compact_imp_countably_compact)
  then show "compact s"
  proof (rule countably_compact_imp_compact)
    show "countable K"
      unfolding K_def using f
      by (auto intro: countable_finite countable_subset countable_rat
               intro!: countable_image countable_SIGMA countable_UN)
    show "\<forall>b\<in>K. open b" by (auto simp: K_def)
  next
    fix T x
    assume T: "open T" "x \<in> T" and x: "x \<in> s"
    from openE[OF T] obtain e where "0 < e" "ball x e \<subseteq> T"
      by auto
    then have "0 < e / 2" "ball x (e / 2) \<subseteq> T"
      by auto
    from Rats_dense_in_real[OF `0 < e / 2`] obtain r where "r \<in> \<rat>" "0 < r" "r < e / 2"
      by auto
    from f[rule_format, of r] `0 < r` `x \<in> s` obtain k where "k \<in> f r" "x \<in> ball k r"
      unfolding Union_image_eq by auto
    from `r \<in> \<rat>` `0 < r` `k \<in> f r` have "ball k r \<in> K"
      by (auto simp: K_def)
    then show "\<exists>b\<in>K. x \<in> b \<and> b \<inter> s \<subseteq> T"
    proof (rule bexI[rotated], safe)
      fix y
      assume "y \<in> ball k r"
      with `r < e / 2` `x \<in> ball k r` have "dist x y < e"
        by (intro dist_double[where x = k and d=e]) (auto simp: dist_commute)
      with `ball x e \<subseteq> T` show "y \<in> T"
        by auto
    next
      show "x \<in> ball k r" by fact
    qed
  qed
qed

lemma compact_eq_seq_compact_metric:
  "compact (s :: 'a::metric_space set) \<longleftrightarrow> seq_compact s"
  using compact_imp_seq_compact seq_compact_imp_heine_borel by blast

lemma compact_def:
  "compact (S :: 'a::metric_space set) \<longleftrightarrow>
   (\<forall>f. (\<forall>n. f n \<in> S) \<longrightarrow> (\<exists>l\<in>S. \<exists>r. subseq r \<and> (f \<circ> r) ----> l))"
  unfolding compact_eq_seq_compact_metric seq_compact_def by auto

subsubsection {* Complete the chain of compactness variants *}

lemma compact_eq_bolzano_weierstrass:
  fixes s :: "'a::metric_space set"
  shows "compact s \<longleftrightarrow> (\<forall>t. infinite t \<and> t \<subseteq> s --> (\<exists>x \<in> s. x islimpt t))"
  (is "?lhs = ?rhs")
proof
  assume ?lhs
  then show ?rhs
    using heine_borel_imp_bolzano_weierstrass[of s] by auto
next
  assume ?rhs
  then show ?lhs
    unfolding compact_eq_seq_compact_metric by (rule bolzano_weierstrass_imp_seq_compact)
qed

lemma bolzano_weierstrass_imp_bounded:
  "\<forall>t. infinite t \<and> t \<subseteq> s \<longrightarrow> (\<exists>x \<in> s. x islimpt t) \<Longrightarrow> bounded s"
  using compact_imp_bounded unfolding compact_eq_bolzano_weierstrass .

subsection {* Metric spaces with the Heine-Borel property *}

text {*
  A metric space (or topological vector space) is said to have the
  Heine-Borel property if every closed and bounded subset is compact.
*}

class heine_borel = metric_space +
  assumes bounded_imp_convergent_subsequence:
    "bounded (range f) \<Longrightarrow> \<exists>l r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"

lemma bounded_closed_imp_seq_compact:
  fixes s::"'a::heine_borel set"
  assumes "bounded s"
    and "closed s"
  shows "seq_compact s"
proof (unfold seq_compact_def, clarify)
  fix f :: "nat \<Rightarrow> 'a"
  assume f: "\<forall>n. f n \<in> s"
  with `bounded s` have "bounded (range f)"
    by (auto intro: bounded_subset)
  obtain l r where r: "subseq r" and l: "((f \<circ> r) ---> l) sequentially"
    using bounded_imp_convergent_subsequence [OF `bounded (range f)`] by auto
  from f have fr: "\<forall>n. (f \<circ> r) n \<in> s"
    by simp
  have "l \<in> s" using `closed s` fr l
    by (rule closed_sequentially)
  show "\<exists>l\<in>s. \<exists>r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"
    using `l \<in> s` r l by blast
qed

lemma compact_eq_bounded_closed:
  fixes s :: "'a::heine_borel set"
  shows "compact s \<longleftrightarrow> bounded s \<and> closed s"
  (is "?lhs = ?rhs")
proof
  assume ?lhs
  then show ?rhs
    using compact_imp_closed compact_imp_bounded
    by blast
next
  assume ?rhs
  then show ?lhs
    using bounded_closed_imp_seq_compact[of s]
    unfolding compact_eq_seq_compact_metric
    by auto
qed

(* TODO: is this lemma necessary? *)
lemma bounded_increasing_convergent:
  fixes s :: "nat \<Rightarrow> real"
  shows "bounded {s n| n. True} \<Longrightarrow> \<forall>n. s n \<le> s (Suc n) \<Longrightarrow> \<exists>l. s ----> l"
  using Bseq_mono_convergent[of s] incseq_Suc_iff[of s]
  by (auto simp: image_def Bseq_eq_bounded convergent_def incseq_def)

instance real :: heine_borel
proof
  fix f :: "nat \<Rightarrow> real"
  assume f: "bounded (range f)"
  obtain r where r: "subseq r" "monoseq (f \<circ> r)"
    unfolding comp_def by (metis seq_monosub)
  then have "Bseq (f \<circ> r)"
    unfolding Bseq_eq_bounded using f by (auto intro: bounded_subset)
  with r show "\<exists>l r. subseq r \<and> (f \<circ> r) ----> l"
    using Bseq_monoseq_convergent[of "f \<circ> r"] by (auto simp: convergent_def)
qed

lemma compact_lemma:
  fixes f :: "nat \<Rightarrow> 'a::euclidean_space"
  assumes "bounded (range f)"
  shows "\<forall>d\<subseteq>Basis. \<exists>l::'a. \<exists> r.
    subseq r \<and> (\<forall>e>0. eventually (\<lambda>n. \<forall>i\<in>d. dist (f (r n) \<bullet> i) (l \<bullet> i) < e) sequentially)"
proof safe
  fix d :: "'a set"
  assume d: "d \<subseteq> Basis"
  with finite_Basis have "finite d"
    by (blast intro: finite_subset)
  from this d show "\<exists>l::'a. \<exists>r. subseq r \<and>
    (\<forall>e>0. eventually (\<lambda>n. \<forall>i\<in>d. dist (f (r n) \<bullet> i) (l \<bullet> i) < e) sequentially)"
  proof (induct d)
    case empty
    then show ?case
      unfolding subseq_def by auto
  next
    case (insert k d)
    have k[intro]: "k \<in> Basis"
      using insert by auto
    have s': "bounded ((\<lambda>x. x \<bullet> k) ` range f)"
      using `bounded (range f)`
      by (auto intro!: bounded_linear_image bounded_linear_inner_left)
    obtain l1::"'a" and r1 where r1: "subseq r1"
      and lr1: "\<forall>e > 0. eventually (\<lambda>n. \<forall>i\<in>d. dist (f (r1 n) \<bullet> i) (l1 \<bullet> i) < e) sequentially"
      using insert(3) using insert(4) by auto
    have f': "\<forall>n. f (r1 n) \<bullet> k \<in> (\<lambda>x. x \<bullet> k) ` range f"
      by simp
    have "bounded (range (\<lambda>i. f (r1 i) \<bullet> k))"
      by (metis (lifting) bounded_subset f' image_subsetI s')
    then obtain l2 r2 where r2:"subseq r2" and lr2:"((\<lambda>i. f (r1 (r2 i)) \<bullet> k) ---> l2) sequentially"
      using bounded_imp_convergent_subsequence[of "\<lambda>i. f (r1 i) \<bullet> k"]
      by (auto simp: o_def)
    def r \<equiv> "r1 \<circ> r2"
    have r:"subseq r"
      using r1 and r2 unfolding r_def o_def subseq_def by auto
    moreover
    def l \<equiv> "(\<Sum>i\<in>Basis. (if i = k then l2 else l1\<bullet>i) *\<^sub>R i)::'a"
    {
      fix e::real
      assume "e > 0"
      from lr1 `e > 0` have N1: "eventually (\<lambda>n. \<forall>i\<in>d. dist (f (r1 n) \<bullet> i) (l1 \<bullet> i) < e) sequentially"
        by blast
      from lr2 `e > 0` have N2:"eventually (\<lambda>n. dist (f (r1 (r2 n)) \<bullet> k) l2 < e) sequentially"
        by (rule tendstoD)
      from r2 N1 have N1': "eventually (\<lambda>n. \<forall>i\<in>d. dist (f (r1 (r2 n)) \<bullet> i) (l1 \<bullet> i) < e) sequentially"
        by (rule eventually_subseq)
      have "eventually (\<lambda>n. \<forall>i\<in>(insert k d). dist (f (r n) \<bullet> i) (l \<bullet> i) < e) sequentially"
        using N1' N2
        by eventually_elim (insert insert.prems, auto simp: l_def r_def o_def)
    }
    ultimately show ?case by auto
  qed
qed

instance euclidean_space \<subseteq> heine_borel
proof
  fix f :: "nat \<Rightarrow> 'a"
  assume f: "bounded (range f)"
  then obtain l::'a and r where r: "subseq r"
    and l: "\<forall>e>0. eventually (\<lambda>n. \<forall>i\<in>Basis. dist (f (r n) \<bullet> i) (l \<bullet> i) < e) sequentially"
    using compact_lemma [OF f] by blast
  {
    fix e::real
    assume "e > 0"
    then have "e / real_of_nat DIM('a) > 0"
      by (auto intro!: divide_pos_pos DIM_positive)
    with l have "eventually (\<lambda>n. \<forall>i\<in>Basis. dist (f (r n) \<bullet> i) (l \<bullet> i) < e / (real_of_nat DIM('a))) sequentially"
      by simp
    moreover
    {
      fix n
      assume n: "\<forall>i\<in>Basis. dist (f (r n) \<bullet> i) (l \<bullet> i) < e / (real_of_nat DIM('a))"
      have "dist (f (r n)) l \<le> (\<Sum>i\<in>Basis. dist (f (r n) \<bullet> i) (l \<bullet> i))"
        apply (subst euclidean_dist_l2)
        using zero_le_dist
        apply (rule setL2_le_setsum)
        done
      also have "\<dots> < (\<Sum>i\<in>(Basis::'a set). e / (real_of_nat DIM('a)))"
        apply (rule setsum_strict_mono)
        using n
        apply auto
        done
      finally have "dist (f (r n)) l < e"
        by auto
    }
    ultimately have "eventually (\<lambda>n. dist (f (r n)) l < e) sequentially"
      by (rule eventually_elim1)
  }
  then have *: "((f \<circ> r) ---> l) sequentially"
    unfolding o_def tendsto_iff by simp
  with r show "\<exists>l r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"
    by auto
qed

lemma bounded_fst: "bounded s \<Longrightarrow> bounded (fst ` s)"
  unfolding bounded_def
  apply clarify
  apply (rule_tac x="a" in exI)
  apply (rule_tac x="e" in exI)
  apply clarsimp
  apply (drule (1) bspec)
  apply (simp add: dist_Pair_Pair)
  apply (erule order_trans [OF real_sqrt_sum_squares_ge1])
  done

lemma bounded_snd: "bounded s \<Longrightarrow> bounded (snd ` s)"
  unfolding bounded_def
  apply clarify
  apply (rule_tac x="b" in exI)
  apply (rule_tac x="e" in exI)
  apply clarsimp
  apply (drule (1) bspec)
  apply (simp add: dist_Pair_Pair)
  apply (erule order_trans [OF real_sqrt_sum_squares_ge2])
  done

instance prod :: (heine_borel, heine_borel) heine_borel
proof
  fix f :: "nat \<Rightarrow> 'a \<times> 'b"
  assume f: "bounded (range f)"
  from f have s1: "bounded (range (fst \<circ> f))"
    unfolding image_comp by (rule bounded_fst)
  obtain l1 r1 where r1: "subseq r1" and l1: "(\<lambda>n. fst (f (r1 n))) ----> l1"
    using bounded_imp_convergent_subsequence [OF s1] unfolding o_def by fast
  from f have s2: "bounded (range (snd \<circ> f \<circ> r1))"
    by (auto simp add: image_comp intro: bounded_snd bounded_subset)
  obtain l2 r2 where r2: "subseq r2" and l2: "((\<lambda>n. snd (f (r1 (r2 n)))) ---> l2) sequentially"
    using bounded_imp_convergent_subsequence [OF s2]
    unfolding o_def by fast
  have l1': "((\<lambda>n. fst (f (r1 (r2 n)))) ---> l1) sequentially"
    using LIMSEQ_subseq_LIMSEQ [OF l1 r2] unfolding o_def .
  have l: "((f \<circ> (r1 \<circ> r2)) ---> (l1, l2)) sequentially"
    using tendsto_Pair [OF l1' l2] unfolding o_def by simp
  have r: "subseq (r1 \<circ> r2)"
    using r1 r2 unfolding subseq_def by simp
  show "\<exists>l r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"
    using l r by fast
qed

subsubsection {* Completeness *}

definition complete :: "'a::metric_space set \<Rightarrow> bool"
  where "complete s \<longleftrightarrow> (\<forall>f. (\<forall>n. f n \<in> s) \<and> Cauchy f \<longrightarrow> (\<exists>l\<in>s. f ----> l))"

lemma completeI:
  assumes "\<And>f. \<forall>n. f n \<in> s \<Longrightarrow> Cauchy f \<Longrightarrow> \<exists>l\<in>s. f ----> l"
  shows "complete s"
  using assms unfolding complete_def by fast

lemma completeE:
  assumes "complete s" and "\<forall>n. f n \<in> s" and "Cauchy f"
  obtains l where "l \<in> s" and "f ----> l"
  using assms unfolding complete_def by fast

lemma compact_imp_complete:
  assumes "compact s"
  shows "complete s"
proof -
  {
    fix f
    assume as: "(\<forall>n::nat. f n \<in> s)" "Cauchy f"
    from as(1) obtain l r where lr: "l\<in>s" "subseq r" "(f \<circ> r) ----> l"
      using assms unfolding compact_def by blast

    note lr' = seq_suble [OF lr(2)]

    {
      fix e :: real
      assume "e > 0"
      from as(2) obtain N where N:"\<forall>m n. N \<le> m \<and> N \<le> n \<longrightarrow> dist (f m) (f n) < e/2"
        unfolding cauchy_def
        using `e > 0`
        apply (erule_tac x="e/2" in allE)
        apply auto
        done
      from lr(3)[unfolded LIMSEQ_def, THEN spec[where x="e/2"]]
      obtain M where M:"\<forall>n\<ge>M. dist ((f \<circ> r) n) l < e/2"
        using `e > 0` by auto
      {
        fix n :: nat
        assume n: "n \<ge> max N M"
        have "dist ((f \<circ> r) n) l < e/2"
          using n M by auto
        moreover have "r n \<ge> N"
          using lr'[of n] n by auto
        then have "dist (f n) ((f \<circ> r) n) < e / 2"
          using N and n by auto
        ultimately have "dist (f n) l < e"
          using dist_triangle_half_r[of "f (r n)" "f n" e l]
          by (auto simp add: dist_commute)
      }
      then have "\<exists>N. \<forall>n\<ge>N. dist (f n) l < e" by blast
    }
    then have "\<exists>l\<in>s. (f ---> l) sequentially" using `l\<in>s`
      unfolding LIMSEQ_def by auto
  }
  then show ?thesis unfolding complete_def by auto
qed

lemma nat_approx_posE:
  fixes e::real
  assumes "0 < e"
  obtains n :: nat where "1 / (Suc n) < e"
proof atomize_elim
  have " 1 / real (Suc (nat (ceiling (1/e)))) < 1 / (ceiling (1/e))"
    by (rule divide_strict_left_mono) (auto intro!: mult_pos_pos simp: `0 < e`)
  also have "1 / (ceiling (1/e)) \<le> 1 / (1/e)"
    by (rule divide_left_mono) (auto intro!: divide_pos_pos simp: `0 < e`)
  also have "\<dots> = e" by simp
  finally show  "\<exists>n. 1 / real (Suc n) < e" ..
qed

lemma compact_eq_totally_bounded:
  "compact s \<longleftrightarrow> complete s \<and> (\<forall>e>0. \<exists>k. finite k \<and> s \<subseteq> (\<Union>((\<lambda>x. ball x e) ` k)))"
    (is "_ \<longleftrightarrow> ?rhs")
proof
  assume assms: "?rhs"
  then obtain k where k: "\<And>e. 0 < e \<Longrightarrow> finite (k e)" "\<And>e. 0 < e \<Longrightarrow> s \<subseteq> (\<Union>x\<in>k e. ball x e)"
    by (auto simp: choice_iff')

  show "compact s"
  proof cases
    assume "s = {}"
    then show "compact s" by (simp add: compact_def)
  next
    assume "s \<noteq> {}"
    show ?thesis
      unfolding compact_def
    proof safe
      fix f :: "nat \<Rightarrow> 'a"
      assume f: "\<forall>n. f n \<in> s"

      def e \<equiv> "\<lambda>n. 1 / (2 * Suc n)"
      then have [simp]: "\<And>n. 0 < e n" by auto
      def B \<equiv> "\<lambda>n U. SOME b. infinite {n. f n \<in> b} \<and> (\<exists>x. b \<subseteq> ball x (e n) \<inter> U)"
      {
        fix n U
        assume "infinite {n. f n \<in> U}"
        then have "\<exists>b\<in>k (e n). infinite {i\<in>{n. f n \<in> U}. f i \<in> ball b (e n)}"
          using k f by (intro pigeonhole_infinite_rel) (auto simp: subset_eq)
        then obtain a where
          "a \<in> k (e n)"
          "infinite {i \<in> {n. f n \<in> U}. f i \<in> ball a (e n)}" ..
        then have "\<exists>b. infinite {i. f i \<in> b} \<and> (\<exists>x. b \<subseteq> ball x (e n) \<inter> U)"
          by (intro exI[of _ "ball a (e n) \<inter> U"] exI[of _ a]) (auto simp: ac_simps)
        from someI_ex[OF this]
        have "infinite {i. f i \<in> B n U}" "\<exists>x. B n U \<subseteq> ball x (e n) \<inter> U"
          unfolding B_def by auto
      }
      note B = this

      def F \<equiv> "rec_nat (B 0 UNIV) B"
      {
        fix n
        have "infinite {i. f i \<in> F n}"
          by (induct n) (auto simp: F_def B)
      }
      then have F: "\<And>n. \<exists>x. F (Suc n) \<subseteq> ball x (e n) \<inter> F n"
        using B by (simp add: F_def)
      then have F_dec: "\<And>m n. m \<le> n \<Longrightarrow> F n \<subseteq> F m"
        using decseq_SucI[of F] by (auto simp: decseq_def)

      obtain sel where sel: "\<And>k i. i < sel k i" "\<And>k i. f (sel k i) \<in> F k"
      proof (atomize_elim, unfold all_conj_distrib[symmetric], intro choice allI)
        fix k i
        have "infinite ({n. f n \<in> F k} - {.. i})"
          using `infinite {n. f n \<in> F k}` by auto
        from infinite_imp_nonempty[OF this]
        show "\<exists>x>i. f x \<in> F k"
          by (simp add: set_eq_iff not_le conj_commute)
      qed

      def t \<equiv> "rec_nat (sel 0 0) (\<lambda>n i. sel (Suc n) i)"
      have "subseq t"
        unfolding subseq_Suc_iff by (simp add: t_def sel)
      moreover have "\<forall>i. (f \<circ> t) i \<in> s"
        using f by auto
      moreover
      {
        fix n
        have "(f \<circ> t) n \<in> F n"
          by (cases n) (simp_all add: t_def sel)
      }
      note t = this

      have "Cauchy (f \<circ> t)"
      proof (safe intro!: metric_CauchyI exI elim!: nat_approx_posE)
        fix r :: real and N n m
        assume "1 / Suc N < r" "Suc N \<le> n" "Suc N \<le> m"
        then have "(f \<circ> t) n \<in> F (Suc N)" "(f \<circ> t) m \<in> F (Suc N)" "2 * e N < r"
          using F_dec t by (auto simp: e_def field_simps real_of_nat_Suc)
        with F[of N] obtain x where "dist x ((f \<circ> t) n) < e N" "dist x ((f \<circ> t) m) < e N"
          by (auto simp: subset_eq)
        with dist_triangle[of "(f \<circ> t) m" "(f \<circ> t) n" x] `2 * e N < r`
        show "dist ((f \<circ> t) m) ((f \<circ> t) n) < r"
          by (simp add: dist_commute)
      qed

      ultimately show "\<exists>l\<in>s. \<exists>r. subseq r \<and> (f \<circ> r) ----> l"
        using assms unfolding complete_def by blast
    qed
  qed
qed (metis compact_imp_complete compact_imp_seq_compact seq_compact_imp_totally_bounded)

lemma cauchy: "Cauchy s \<longleftrightarrow> (\<forall>e>0.\<exists> N::nat. \<forall>n\<ge>N. dist(s n)(s N) < e)" (is "?lhs = ?rhs")
proof -
  {
    assume ?rhs
    {
      fix e::real
      assume "e>0"
      with `?rhs` obtain N where N:"\<forall>n\<ge>N. dist (s n) (s N) < e/2"
        by (erule_tac x="e/2" in allE) auto
      {
        fix n m
        assume nm:"N \<le> m \<and> N \<le> n"
        then have "dist (s m) (s n) < e" using N
          using dist_triangle_half_l[of "s m" "s N" "e" "s n"]
          by blast
      }
      then have "\<exists>N. \<forall>m n. N \<le> m \<and> N \<le> n \<longrightarrow> dist (s m) (s n) < e"
        by blast
    }
    then have ?lhs
      unfolding cauchy_def
      by blast
  }
  then show ?thesis
    unfolding cauchy_def
    using dist_triangle_half_l
    by blast
qed

lemma cauchy_imp_bounded:
  assumes "Cauchy s"
  shows "bounded (range s)"
proof -
  from assms obtain N :: nat where "\<forall>m n. N \<le> m \<and> N \<le> n \<longrightarrow> dist (s m) (s n) < 1"
    unfolding cauchy_def
    apply (erule_tac x= 1 in allE)
    apply auto
    done
  then have N:"\<forall>n. N \<le> n \<longrightarrow> dist (s N) (s n) < 1" by auto
  moreover
  have "bounded (s ` {0..N})"
    using finite_imp_bounded[of "s ` {1..N}"] by auto
  then obtain a where a:"\<forall>x\<in>s ` {0..N}. dist (s N) x \<le> a"
    unfolding bounded_any_center [where a="s N"] by auto
  ultimately show "?thesis"
    unfolding bounded_any_center [where a="s N"]
    apply (rule_tac x="max a 1" in exI)
    apply auto
    apply (erule_tac x=y in allE)
    apply (erule_tac x=y in ballE)
    apply auto
    done
qed

instance heine_borel < complete_space
proof
  fix f :: "nat \<Rightarrow> 'a" assume "Cauchy f"
  then have "bounded (range f)"
    by (rule cauchy_imp_bounded)
  then have "compact (closure (range f))"
    unfolding compact_eq_bounded_closed by auto
  then have "complete (closure (range f))"
    by (rule compact_imp_complete)
  moreover have "\<forall>n. f n \<in> closure (range f)"
    using closure_subset [of "range f"] by auto
  ultimately have "\<exists>l\<in>closure (range f). (f ---> l) sequentially"
    using `Cauchy f` unfolding complete_def by auto
  then show "convergent f"
    unfolding convergent_def by auto
qed

instance euclidean_space \<subseteq> banach ..

lemma complete_UNIV: "complete (UNIV :: ('a::complete_space) set)"
proof (rule completeI)
  fix f :: "nat \<Rightarrow> 'a" assume "Cauchy f"
  then have "convergent f" by (rule Cauchy_convergent)
  then show "\<exists>l\<in>UNIV. f ----> l" unfolding convergent_def by simp
qed

lemma complete_imp_closed:
  assumes "complete s"
  shows "closed s"
proof (unfold closed_sequential_limits, clarify)
  fix f x assume "\<forall>n. f n \<in> s" and "f ----> x"
  from `f ----> x` have "Cauchy f"
    by (rule LIMSEQ_imp_Cauchy)
  with `complete s` and `\<forall>n. f n \<in> s` obtain l where "l \<in> s" and "f ----> l"
    by (rule completeE)
  from `f ----> x` and `f ----> l` have "x = l"
    by (rule LIMSEQ_unique)
  with `l \<in> s` show "x \<in> s"
    by simp
qed

lemma complete_inter_closed:
  assumes "complete s" and "closed t"
  shows "complete (s \<inter> t)"
proof (rule completeI)
  fix f assume "\<forall>n. f n \<in> s \<inter> t" and "Cauchy f"
  then have "\<forall>n. f n \<in> s" and "\<forall>n. f n \<in> t"
    by simp_all
  from `complete s` obtain l where "l \<in> s" and "f ----> l"
    using `\<forall>n. f n \<in> s` and `Cauchy f` by (rule completeE)
  from `closed t` and `\<forall>n. f n \<in> t` and `f ----> l` have "l \<in> t"
    by (rule closed_sequentially)
  with `l \<in> s` and `f ----> l` show "\<exists>l\<in>s \<inter> t. f ----> l"
    by fast
qed

lemma complete_closed_subset:
  assumes "closed s" and "s \<subseteq> t" and "complete t"
  shows "complete s"
  using assms complete_inter_closed [of t s] by (simp add: Int_absorb1)

lemma complete_eq_closed:
  fixes s :: "('a::complete_space) set"
  shows "complete s \<longleftrightarrow> closed s"
proof
  assume "closed s" then show "complete s"
    using subset_UNIV complete_UNIV by (rule complete_closed_subset)
next
  assume "complete s" then show "closed s"
    by (rule complete_imp_closed)
qed

lemma convergent_eq_cauchy:
  fixes s :: "nat \<Rightarrow> 'a::complete_space"
  shows "(\<exists>l. (s ---> l) sequentially) \<longleftrightarrow> Cauchy s"
  unfolding Cauchy_convergent_iff convergent_def ..

lemma convergent_imp_bounded:
  fixes s :: "nat \<Rightarrow> 'a::metric_space"
  shows "(s ---> l) sequentially \<Longrightarrow> bounded (range s)"
  by (intro cauchy_imp_bounded LIMSEQ_imp_Cauchy)

lemma compact_cball[simp]:
  fixes x :: "'a::heine_borel"
  shows "compact (cball x e)"
  using compact_eq_bounded_closed bounded_cball closed_cball
  by blast

lemma compact_frontier_bounded[intro]:
  fixes s :: "'a::heine_borel set"
  shows "bounded s \<Longrightarrow> compact (frontier s)"
  unfolding frontier_def
  using compact_eq_bounded_closed
  by blast

lemma compact_frontier[intro]:
  fixes s :: "'a::heine_borel set"
  shows "compact s \<Longrightarrow> compact (frontier s)"
  using compact_eq_bounded_closed compact_frontier_bounded
  by blast

lemma frontier_subset_compact:
  fixes s :: "'a::heine_borel set"
  shows "compact s \<Longrightarrow> frontier s \<subseteq> s"
  using frontier_subset_closed compact_eq_bounded_closed
  by blast

subsection {* Bounded closed nest property (proof does not use Heine-Borel) *}

lemma bounded_closed_nest:
  fixes s :: "nat \<Rightarrow> ('a::heine_borel) set"
  assumes "\<forall>n. closed (s n)"
    and "\<forall>n. s n \<noteq> {}"
    and "\<forall>m n. m \<le> n \<longrightarrow> s n \<subseteq> s m"
    and "bounded (s 0)"
  shows "\<exists>a. \<forall>n. a \<in> s n"
proof -
  from assms(2) obtain x where x: "\<forall>n. x n \<in> s n"
    using choice[of "\<lambda>n x. x \<in> s n"] by auto
  from assms(4,1) have "seq_compact (s 0)"
    by (simp add: bounded_closed_imp_seq_compact)
  then obtain l r where lr: "l \<in> s 0" "subseq r" "(x \<circ> r) ----> l"
    using x and assms(3) unfolding seq_compact_def by blast
  have "\<forall>n. l \<in> s n"
  proof
    fix n :: nat
    have "closed (s n)"
      using assms(1) by simp
    moreover have "\<forall>i. (x \<circ> r) i \<in> s i"
      using x and assms(3) and lr(2) [THEN seq_suble] by auto
    then have "\<forall>i. (x \<circ> r) (i + n) \<in> s n"
      using assms(3) by (fast intro!: le_add2)
    moreover have "(\<lambda>i. (x \<circ> r) (i + n)) ----> l"
      using lr(3) by (rule LIMSEQ_ignore_initial_segment)
    ultimately show "l \<in> s n"
      by (rule closed_sequentially)
  qed
  then show ?thesis ..
qed

text {* Decreasing case does not even need compactness, just completeness. *}

lemma decreasing_closed_nest:
  fixes s :: "nat \<Rightarrow> ('a::complete_space) set"
  assumes
    "\<forall>n. closed (s n)"
    "\<forall>n. s n \<noteq> {}"
    "\<forall>m n. m \<le> n \<longrightarrow> s n \<subseteq> s m"
    "\<forall>e>0. \<exists>n. \<forall>x\<in>s n. \<forall>y\<in>s n. dist x y < e"
  shows "\<exists>a. \<forall>n. a \<in> s n"
proof -
  have "\<forall>n. \<exists>x. x \<in> s n"
    using assms(2) by auto
  then have "\<exists>t. \<forall>n. t n \<in> s n"
    using choice[of "\<lambda>n x. x \<in> s n"] by auto
  then obtain t where t: "\<forall>n. t n \<in> s n" by auto
  {
    fix e :: real
    assume "e > 0"
    then obtain N where N:"\<forall>x\<in>s N. \<forall>y\<in>s N. dist x y < e"
      using assms(4) by auto
    {
      fix m n :: nat
      assume "N \<le> m \<and> N \<le> n"
      then have "t m \<in> s N" "t n \<in> s N"
        using assms(3) t unfolding  subset_eq t by blast+
      then have "dist (t m) (t n) < e"
        using N by auto
    }
    then have "\<exists>N. \<forall>m n. N \<le> m \<and> N \<le> n \<longrightarrow> dist (t m) (t n) < e"
      by auto
  }
  then have "Cauchy t"
    unfolding cauchy_def by auto
  then obtain l where l:"(t ---> l) sequentially"
    using complete_UNIV unfolding complete_def by auto
  {
    fix n :: nat
    {
      fix e :: real
      assume "e > 0"
      then obtain N :: nat where N: "\<forall>n\<ge>N. dist (t n) l < e"
        using l[unfolded LIMSEQ_def] by auto
      have "t (max n N) \<in> s n"
        using assms(3)
        unfolding subset_eq
        apply (erule_tac x=n in allE)
        apply (erule_tac x="max n N" in allE)
        using t
        apply auto
        done
      then have "\<exists>y\<in>s n. dist y l < e"
        apply (rule_tac x="t (max n N)" in bexI)
        using N
        apply auto
        done
    }
    then have "l \<in> s n"
      using closed_approachable[of "s n" l] assms(1) by auto
  }
  then show ?thesis by auto
qed

text {* Strengthen it to the intersection actually being a singleton. *}

lemma decreasing_closed_nest_sing:
  fixes s :: "nat \<Rightarrow> 'a::complete_space set"
  assumes
    "\<forall>n. closed(s n)"
    "\<forall>n. s n \<noteq> {}"
    "\<forall>m n. m \<le> n \<longrightarrow> s n \<subseteq> s m"
    "\<forall>e>0. \<exists>n. \<forall>x \<in> (s n). \<forall> y\<in>(s n). dist x y < e"
  shows "\<exists>a. \<Inter>(range s) = {a}"
proof -
  obtain a where a: "\<forall>n. a \<in> s n"
    using decreasing_closed_nest[of s] using assms by auto
  {
    fix b
    assume b: "b \<in> \<Inter>(range s)"
    {
      fix e :: real
      assume "e > 0"
      then have "dist a b < e"
        using assms(4) and b and a by blast
    }
    then have "dist a b = 0"
      by (metis dist_eq_0_iff dist_nz less_le)
  }
  with a have "\<Inter>(range s) = {a}"
    unfolding image_def by auto
  then show ?thesis ..
qed

text{* Cauchy-type criteria for uniform convergence. *}

lemma uniformly_convergent_eq_cauchy:
  fixes s::"nat \<Rightarrow> 'b \<Rightarrow> 'a::complete_space"
  shows
    "(\<exists>l. \<forall>e>0. \<exists>N. \<forall>n x. N \<le> n \<and> P x \<longrightarrow> dist(s n x)(l x) < e) \<longleftrightarrow>
      (\<forall>e>0. \<exists>N. \<forall>m n x. N \<le> m \<and> N \<le> n \<and> P x  \<longrightarrow> dist (s m x) (s n x) < e)"
  (is "?lhs = ?rhs")
proof
  assume ?lhs
  then obtain l where l:"\<forall>e>0. \<exists>N. \<forall>n x. N \<le> n \<and> P x \<longrightarrow> dist (s n x) (l x) < e"
    by auto
  {
    fix e :: real
    assume "e > 0"
    then obtain N :: nat where N: "\<forall>n x. N \<le> n \<and> P x \<longrightarrow> dist (s n x) (l x) < e / 2"
      using l[THEN spec[where x="e/2"]] by auto
    {
      fix n m :: nat and x :: "'b"
      assume "N \<le> m \<and> N \<le> n \<and> P x"
      then have "dist (s m x) (s n x) < e"
        using N[THEN spec[where x=m], THEN spec[where x=x]]
        using N[THEN spec[where x=n], THEN spec[where x=x]]
        using dist_triangle_half_l[of "s m x" "l x" e "s n x"] by auto
    }
    then have "\<exists>N. \<forall>m n x. N \<le> m \<and> N \<le> n \<and> P x  --> dist (s m x) (s n x) < e"  by auto
  }
  then show ?rhs by auto
next
  assume ?rhs
  then have "\<forall>x. P x \<longrightarrow> Cauchy (\<lambda>n. s n x)"
    unfolding cauchy_def
    apply auto
    apply (erule_tac x=e in allE)
    apply auto
    done
  then obtain l where l: "\<forall>x. P x \<longrightarrow> ((\<lambda>n. s n x) ---> l x) sequentially"
    unfolding convergent_eq_cauchy[symmetric]
    using choice[of "\<lambda>x l. P x \<longrightarrow> ((\<lambda>n. s n x) ---> l) sequentially"]
    by auto
  {
    fix e :: real
    assume "e > 0"
    then obtain N where N:"\<forall>m n x. N \<le> m \<and> N \<le> n \<and> P x \<longrightarrow> dist (s m x) (s n x) < e/2"
      using `?rhs`[THEN spec[where x="e/2"]] by auto
    {
      fix x
      assume "P x"
      then obtain M where M:"\<forall>n\<ge>M. dist (s n x) (l x) < e/2"
        using l[THEN spec[where x=x], unfolded LIMSEQ_def] and `e > 0`
        by (auto elim!: allE[where x="e/2"])
      fix n :: nat
      assume "n \<ge> N"
      then have "dist(s n x)(l x) < e"
        using `P x`and N[THEN spec[where x=n], THEN spec[where x="N+M"], THEN spec[where x=x]]
        using M[THEN spec[where x="N+M"]] and dist_triangle_half_l[of "s n x" "s (N+M) x" e "l x"]
        by (auto simp add: dist_commute)
    }
    then have "\<exists>N. \<forall>n x. N \<le> n \<and> P x \<longrightarrow> dist(s n x)(l x) < e"
      by auto
  }
  then show ?lhs by auto
qed

lemma uniformly_cauchy_imp_uniformly_convergent:
  fixes s :: "nat \<Rightarrow> 'a \<Rightarrow> 'b::complete_space"
  assumes "\<forall>e>0.\<exists>N. \<forall>m (n::nat) x. N \<le> m \<and> N \<le> n \<and> P x --> dist(s m x)(s n x) < e"
    and "\<forall>x. P x --> (\<forall>e>0. \<exists>N. \<forall>n. N \<le> n \<longrightarrow> dist(s n x)(l x) < e)"
  shows "\<forall>e>0. \<exists>N. \<forall>n x. N \<le> n \<and> P x \<longrightarrow> dist(s n x)(l x) < e"
proof -
  obtain l' where l:"\<forall>e>0. \<exists>N. \<forall>n x. N \<le> n \<and> P x \<longrightarrow> dist (s n x) (l' x) < e"
    using assms(1) unfolding uniformly_convergent_eq_cauchy[symmetric] by auto
  moreover
  {
    fix x
    assume "P x"
    then have "l x = l' x"
      using tendsto_unique[OF trivial_limit_sequentially, of "\<lambda>n. s n x" "l x" "l' x"]
      using l and assms(2) unfolding LIMSEQ_def by blast
  }
  ultimately show ?thesis by auto
qed


subsection {* Continuity *}

text{* Derive the epsilon-delta forms, which we often use as "definitions" *}

lemma continuous_within_eps_delta:
  "continuous (at x within s) f \<longleftrightarrow> (\<forall>e>0. \<exists>d>0. \<forall>x'\<in> s.  dist x' x < d --> dist (f x') (f x) < e)"
  unfolding continuous_within and Lim_within
  apply auto
  unfolding dist_nz[symmetric]
  apply (auto del: allE elim!:allE)
  apply(rule_tac x=d in exI)
  apply auto
  done

lemma continuous_at_eps_delta:
  "continuous (at x) f \<longleftrightarrow> (\<forall>e > 0. \<exists>d > 0. \<forall>x'. dist x' x < d \<longrightarrow> dist (f x') (f x) < e)"
  using continuous_within_eps_delta [of x UNIV f] by simp

text{* Versions in terms of open balls. *}

lemma continuous_within_ball:
  "continuous (at x within s) f \<longleftrightarrow>
    (\<forall>e > 0. \<exists>d > 0. f ` (ball x d \<inter> s) \<subseteq> ball (f x) e)"
  (is "?lhs = ?rhs")
proof
  assume ?lhs
  {
    fix e :: real
    assume "e > 0"
    then obtain d where d: "d>0" "\<forall>xa\<in>s. 0 < dist xa x \<and> dist xa x < d \<longrightarrow> dist (f xa) (f x) < e"
      using `?lhs`[unfolded continuous_within Lim_within] by auto
    {
      fix y
      assume "y \<in> f ` (ball x d \<inter> s)"
      then have "y \<in> ball (f x) e"
        using d(2)
        unfolding dist_nz[symmetric]
        apply (auto simp add: dist_commute)
        apply (erule_tac x=xa in ballE)
        apply auto
        using `e > 0`
        apply auto
        done
    }
    then have "\<exists>d>0. f ` (ball x d \<inter> s) \<subseteq> ball (f x) e"
      using `d > 0`
      unfolding subset_eq ball_def by (auto simp add: dist_commute)
  }
  then show ?rhs by auto
next
  assume ?rhs
  then show ?lhs
    unfolding continuous_within Lim_within ball_def subset_eq
    apply (auto simp add: dist_commute)
    apply (erule_tac x=e in allE)
    apply auto
    done
qed

lemma continuous_at_ball:
  "continuous (at x) f \<longleftrightarrow> (\<forall>e>0. \<exists>d>0. f ` (ball x d) \<subseteq> ball (f x) e)" (is "?lhs = ?rhs")
proof
  assume ?lhs
  then show ?rhs
    unfolding continuous_at Lim_at subset_eq Ball_def Bex_def image_iff mem_ball
    apply auto
    apply (erule_tac x=e in allE)
    apply auto
    apply (rule_tac x=d in exI)
    apply auto
    apply (erule_tac x=xa in allE)
    apply (auto simp add: dist_commute dist_nz)
    unfolding dist_nz[symmetric]
    apply auto
    done
next
  assume ?rhs
  then show ?lhs
    unfolding continuous_at Lim_at subset_eq Ball_def Bex_def image_iff mem_ball
    apply auto
    apply (erule_tac x=e in allE)
    apply auto
    apply (rule_tac x=d in exI)
    apply auto
    apply (erule_tac x="f xa" in allE)
    apply (auto simp add: dist_commute dist_nz)
    done
qed

text{* Define setwise continuity in terms of limits within the set. *}

lemma continuous_on_iff:
  "continuous_on s f \<longleftrightarrow>
    (\<forall>x\<in>s. \<forall>e>0. \<exists>d>0. \<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist (f x') (f x) < e)"
  unfolding continuous_on_def Lim_within
  apply (intro ball_cong [OF refl] all_cong ex_cong)
  apply (rename_tac y, case_tac "y = x")
  apply simp
  apply (simp add: dist_nz)
  done

definition uniformly_continuous_on :: "'a set \<Rightarrow> ('a::metric_space \<Rightarrow> 'b::metric_space) \<Rightarrow> bool"
  where "uniformly_continuous_on s f \<longleftrightarrow>
    (\<forall>e>0. \<exists>d>0. \<forall>x\<in>s. \<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist (f x') (f x) < e)"

text{* Some simple consequential lemmas. *}

lemma uniformly_continuous_imp_continuous:
  "uniformly_continuous_on s f \<Longrightarrow> continuous_on s f"
  unfolding uniformly_continuous_on_def continuous_on_iff by blast

lemma continuous_at_imp_continuous_within:
  "continuous (at x) f \<Longrightarrow> continuous (at x within s) f"
  unfolding continuous_within continuous_at using Lim_at_within by auto

lemma Lim_trivial_limit: "trivial_limit net \<Longrightarrow> (f ---> l) net"
  by simp

lemmas continuous_on = continuous_on_def -- "legacy theorem name"

lemma continuous_within_subset:
  "continuous (at x within s) f \<Longrightarrow> t \<subseteq> s \<Longrightarrow> continuous (at x within t) f"
  unfolding continuous_within by(metis tendsto_within_subset)

lemma continuous_on_interior:
  "continuous_on s f \<Longrightarrow> x \<in> interior s \<Longrightarrow> continuous (at x) f"
  apply (erule interiorE)
  apply (drule (1) continuous_on_subset)
  apply (simp add: continuous_on_eq_continuous_at)
  done

lemma continuous_on_eq:
  "(\<forall>x \<in> s. f x = g x) \<Longrightarrow> continuous_on s f \<Longrightarrow> continuous_on s g"
  unfolding continuous_on_def tendsto_def eventually_at_topological
  by simp

text {* Characterization of various kinds of continuity in terms of sequences. *}

lemma continuous_within_sequentially:
  fixes f :: "'a::metric_space \<Rightarrow> 'b::topological_space"
  shows "continuous (at a within s) f \<longleftrightarrow>
    (\<forall>x. (\<forall>n::nat. x n \<in> s) \<and> (x ---> a) sequentially
         \<longrightarrow> ((f \<circ> x) ---> f a) sequentially)"
  (is "?lhs = ?rhs")
proof
  assume ?lhs
  {
    fix x :: "nat \<Rightarrow> 'a"
    assume x: "\<forall>n. x n \<in> s" "\<forall>e>0. eventually (\<lambda>n. dist (x n) a < e) sequentially"
    fix T :: "'b set"
    assume "open T" and "f a \<in> T"
    with `?lhs` obtain d where "d>0" and d:"\<forall>x\<in>s. 0 < dist x a \<and> dist x a < d \<longrightarrow> f x \<in> T"
      unfolding continuous_within tendsto_def eventually_at by (auto simp: dist_nz)
    have "eventually (\<lambda>n. dist (x n) a < d) sequentially"
      using x(2) `d>0` by simp
    then have "eventually (\<lambda>n. (f \<circ> x) n \<in> T) sequentially"
    proof eventually_elim
      case (elim n)
      then show ?case
        using d x(1) `f a \<in> T` unfolding dist_nz[symmetric] by auto
    qed
  }
  then show ?rhs
    unfolding tendsto_iff tendsto_def by simp
next
  assume ?rhs
  then show ?lhs
    unfolding continuous_within tendsto_def [where l="f a"]
    by (simp add: sequentially_imp_eventually_within)
qed

lemma continuous_at_sequentially:
  fixes f :: "'a::metric_space \<Rightarrow> 'b::topological_space"
  shows "continuous (at a) f \<longleftrightarrow>
    (\<forall>x. (x ---> a) sequentially --> ((f \<circ> x) ---> f a) sequentially)"
  using continuous_within_sequentially[of a UNIV f] by simp

lemma continuous_on_sequentially:
  fixes f :: "'a::metric_space \<Rightarrow> 'b::topological_space"
  shows "continuous_on s f \<longleftrightarrow>
    (\<forall>x. \<forall>a \<in> s. (\<forall>n. x(n) \<in> s) \<and> (x ---> a) sequentially
      --> ((f \<circ> x) ---> f a) sequentially)"
  (is "?lhs = ?rhs")
proof
  assume ?rhs
  then show ?lhs
    using continuous_within_sequentially[of _ s f]
    unfolding continuous_on_eq_continuous_within
    by auto
next
  assume ?lhs
  then show ?rhs
    unfolding continuous_on_eq_continuous_within
    using continuous_within_sequentially[of _ s f]
    by auto
qed

lemma uniformly_continuous_on_sequentially:
  "uniformly_continuous_on s f \<longleftrightarrow> (\<forall>x y. (\<forall>n. x n \<in> s) \<and> (\<forall>n. y n \<in> s) \<and>
                    ((\<lambda>n. dist (x n) (y n)) ---> 0) sequentially
                    \<longrightarrow> ((\<lambda>n. dist (f(x n)) (f(y n))) ---> 0) sequentially)" (is "?lhs = ?rhs")
proof
  assume ?lhs
  {
    fix x y
    assume x: "\<forall>n. x n \<in> s"
      and y: "\<forall>n. y n \<in> s"
      and xy: "((\<lambda>n. dist (x n) (y n)) ---> 0) sequentially"
    {
      fix e :: real
      assume "e > 0"
      then obtain d where "d > 0" and d: "\<forall>x\<in>s. \<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist (f x') (f x) < e"
        using `?lhs`[unfolded uniformly_continuous_on_def, THEN spec[where x=e]] by auto
      obtain N where N: "\<forall>n\<ge>N. dist (x n) (y n) < d"
        using xy[unfolded LIMSEQ_def dist_norm] and `d>0` by auto
      {
        fix n
        assume "n\<ge>N"
        then have "dist (f (x n)) (f (y n)) < e"
          using N[THEN spec[where x=n]]
          using d[THEN bspec[where x="x n"], THEN bspec[where x="y n"]]
          using x and y
          unfolding dist_commute
          by simp
      }
      then have "\<exists>N. \<forall>n\<ge>N. dist (f (x n)) (f (y n)) < e"
        by auto
    }
    then have "((\<lambda>n. dist (f(x n)) (f(y n))) ---> 0) sequentially"
      unfolding LIMSEQ_def and dist_real_def by auto
  }
  then show ?rhs by auto
next
  assume ?rhs
  {
    assume "\<not> ?lhs"
    then obtain e where "e > 0" "\<forall>d>0. \<exists>x\<in>s. \<exists>x'\<in>s. dist x' x < d \<and> \<not> dist (f x') (f x) < e"
      unfolding uniformly_continuous_on_def by auto
    then obtain fa where fa:
      "\<forall>x. 0 < x \<longrightarrow> fst (fa x) \<in> s \<and> snd (fa x) \<in> s \<and> dist (fst (fa x)) (snd (fa x)) < x \<and> \<not> dist (f (fst (fa x))) (f (snd (fa x))) < e"
      using choice[of "\<lambda>d x. d>0 \<longrightarrow> fst x \<in> s \<and> snd x \<in> s \<and> dist (snd x) (fst x) < d \<and> \<not> dist (f (snd x)) (f (fst x)) < e"]
      unfolding Bex_def
      by (auto simp add: dist_commute)
    def x \<equiv> "\<lambda>n::nat. fst (fa (inverse (real n + 1)))"
    def y \<equiv> "\<lambda>n::nat. snd (fa (inverse (real n + 1)))"
    have xyn: "\<forall>n. x n \<in> s \<and> y n \<in> s"
      and xy0: "\<forall>n. dist (x n) (y n) < inverse (real n + 1)"
      and fxy:"\<forall>n. \<not> dist (f (x n)) (f (y n)) < e"
      unfolding x_def and y_def using fa
      by auto
    {
      fix e :: real
      assume "e > 0"
      then obtain N :: nat where "N \<noteq> 0" and N: "0 < inverse (real N) \<and> inverse (real N) < e"
        unfolding real_arch_inv[of e] by auto
      {
        fix n :: nat
        assume "n \<ge> N"
        then have "inverse (real n + 1) < inverse (real N)"
          using real_of_nat_ge_zero and `N\<noteq>0` by auto
        also have "\<dots> < e" using N by auto
        finally have "inverse (real n + 1) < e" by auto
        then have "dist (x n) (y n) < e"
          using xy0[THEN spec[where x=n]] by auto
      }
      then have "\<exists>N. \<forall>n\<ge>N. dist (x n) (y n) < e" by auto
    }
    then have "\<forall>e>0. \<exists>N. \<forall>n\<ge>N. dist (f (x n)) (f (y n)) < e"
      using `?rhs`[THEN spec[where x=x], THEN spec[where x=y]] and xyn
      unfolding LIMSEQ_def dist_real_def by auto
    then have False using fxy and `e>0` by auto
  }
  then show ?lhs
    unfolding uniformly_continuous_on_def by blast
qed

text{* The usual transformation theorems. *}

lemma continuous_transform_within:
  fixes f g :: "'a::metric_space \<Rightarrow> 'b::topological_space"
  assumes "0 < d"
    and "x \<in> s"
    and "\<forall>x' \<in> s. dist x' x < d --> f x' = g x'"
    and "continuous (at x within s) f"
  shows "continuous (at x within s) g"
  unfolding continuous_within
proof (rule Lim_transform_within)
  show "0 < d" by fact
  show "\<forall>x'\<in>s. 0 < dist x' x \<and> dist x' x < d \<longrightarrow> f x' = g x'"
    using assms(3) by auto
  have "f x = g x"
    using assms(1,2,3) by auto
  then show "(f ---> g x) (at x within s)"
    using assms(4) unfolding continuous_within by simp
qed

lemma continuous_transform_at:
  fixes f g :: "'a::metric_space \<Rightarrow> 'b::topological_space"
  assumes "0 < d"
    and "\<forall>x'. dist x' x < d --> f x' = g x'"
    and "continuous (at x) f"
  shows "continuous (at x) g"
  using continuous_transform_within [of d x UNIV f g] assms by simp


subsubsection {* Structural rules for pointwise continuity *}

lemmas continuous_within_id = continuous_ident

lemmas continuous_at_id = isCont_ident

lemma continuous_infdist[continuous_intros]:
  assumes "continuous F f"
  shows "continuous F (\<lambda>x. infdist (f x) A)"
  using assms unfolding continuous_def by (rule tendsto_infdist)

lemma continuous_infnorm[continuous_intros]:
  "continuous F f \<Longrightarrow> continuous F (\<lambda>x. infnorm (f x))"
  unfolding continuous_def by (rule tendsto_infnorm)

lemma continuous_inner[continuous_intros]:
  assumes "continuous F f"
    and "continuous F g"
  shows "continuous F (\<lambda>x. inner (f x) (g x))"
  using assms unfolding continuous_def by (rule tendsto_inner)

lemmas continuous_at_inverse = isCont_inverse

subsubsection {* Structural rules for setwise continuity *}

lemma continuous_on_infnorm[continuous_on_intros]:
  "continuous_on s f \<Longrightarrow> continuous_on s (\<lambda>x. infnorm (f x))"
  unfolding continuous_on by (fast intro: tendsto_infnorm)

lemma continuous_on_inner[continuous_on_intros]:
  fixes g :: "'a::topological_space \<Rightarrow> 'b::real_inner"
  assumes "continuous_on s f"
    and "continuous_on s g"
  shows "continuous_on s (\<lambda>x. inner (f x) (g x))"
  using bounded_bilinear_inner assms
  by (rule bounded_bilinear.continuous_on)

subsubsection {* Structural rules for uniform continuity *}

lemma uniformly_continuous_on_id[continuous_on_intros]:
  "uniformly_continuous_on s (\<lambda>x. x)"
  unfolding uniformly_continuous_on_def by auto

lemma uniformly_continuous_on_const[continuous_on_intros]:
  "uniformly_continuous_on s (\<lambda>x. c)"
  unfolding uniformly_continuous_on_def by simp

lemma uniformly_continuous_on_dist[continuous_on_intros]:
  fixes f g :: "'a::metric_space \<Rightarrow> 'b::metric_space"
  assumes "uniformly_continuous_on s f"
    and "uniformly_continuous_on s g"
  shows "uniformly_continuous_on s (\<lambda>x. dist (f x) (g x))"
proof -
  {
    fix a b c d :: 'b
    have "\<bar>dist a b - dist c d\<bar> \<le> dist a c + dist b d"
      using dist_triangle2 [of a b c] dist_triangle2 [of b c d]
      using dist_triangle3 [of c d a] dist_triangle [of a d b]
      by arith
  } note le = this
  {
    fix x y
    assume f: "(\<lambda>n. dist (f (x n)) (f (y n))) ----> 0"
    assume g: "(\<lambda>n. dist (g (x n)) (g (y n))) ----> 0"
    have "(\<lambda>n. \<bar>dist (f (x n)) (g (x n)) - dist (f (y n)) (g (y n))\<bar>) ----> 0"
      by (rule Lim_transform_bound [OF _ tendsto_add_zero [OF f g]],
        simp add: le)
  }
  then show ?thesis
    using assms unfolding uniformly_continuous_on_sequentially
    unfolding dist_real_def by simp
qed

lemma uniformly_continuous_on_norm[continuous_on_intros]:
  assumes "uniformly_continuous_on s f"
  shows "uniformly_continuous_on s (\<lambda>x. norm (f x))"
  unfolding norm_conv_dist using assms
  by (intro uniformly_continuous_on_dist uniformly_continuous_on_const)

lemma (in bounded_linear) uniformly_continuous_on[continuous_on_intros]:
  assumes "uniformly_continuous_on s g"
  shows "uniformly_continuous_on s (\<lambda>x. f (g x))"
  using assms unfolding uniformly_continuous_on_sequentially
  unfolding dist_norm tendsto_norm_zero_iff diff[symmetric]
  by (auto intro: tendsto_zero)

lemma uniformly_continuous_on_cmul[continuous_on_intros]:
  fixes f :: "'a::metric_space \<Rightarrow> 'b::real_normed_vector"
  assumes "uniformly_continuous_on s f"
  shows "uniformly_continuous_on s (\<lambda>x. c *\<^sub>R f(x))"
  using bounded_linear_scaleR_right assms
  by (rule bounded_linear.uniformly_continuous_on)

lemma dist_minus:
  fixes x y :: "'a::real_normed_vector"
  shows "dist (- x) (- y) = dist x y"
  unfolding dist_norm minus_diff_minus norm_minus_cancel ..

lemma uniformly_continuous_on_minus[continuous_on_intros]:
  fixes f :: "'a::metric_space \<Rightarrow> 'b::real_normed_vector"
  shows "uniformly_continuous_on s f \<Longrightarrow> uniformly_continuous_on s (\<lambda>x. - f x)"
  unfolding uniformly_continuous_on_def dist_minus .

lemma uniformly_continuous_on_add[continuous_on_intros]:
  fixes f g :: "'a::metric_space \<Rightarrow> 'b::real_normed_vector"
  assumes "uniformly_continuous_on s f"
    and "uniformly_continuous_on s g"
  shows "uniformly_continuous_on s (\<lambda>x. f x + g x)"
  using assms
  unfolding uniformly_continuous_on_sequentially
  unfolding dist_norm tendsto_norm_zero_iff add_diff_add
  by (auto intro: tendsto_add_zero)

lemma uniformly_continuous_on_diff[continuous_on_intros]:
  fixes f :: "'a::metric_space \<Rightarrow> 'b::real_normed_vector"
  assumes "uniformly_continuous_on s f"
    and "uniformly_continuous_on s g"
  shows "uniformly_continuous_on s (\<lambda>x. f x - g x)"
  using assms uniformly_continuous_on_add [of s f "- g"]
    by (simp add: fun_Compl_def uniformly_continuous_on_minus)

text{* Continuity of all kinds is preserved under composition. *}

lemmas continuous_at_compose = isCont_o

lemma uniformly_continuous_on_compose[continuous_on_intros]:
  assumes "uniformly_continuous_on s f"  "uniformly_continuous_on (f ` s) g"
  shows "uniformly_continuous_on s (g \<circ> f)"
proof -
  {
    fix e :: real
    assume "e > 0"
    then obtain d where "d > 0"
      and d: "\<forall>x\<in>f ` s. \<forall>x'\<in>f ` s. dist x' x < d \<longrightarrow> dist (g x') (g x) < e"
      using assms(2) unfolding uniformly_continuous_on_def by auto
    obtain d' where "d'>0" "\<forall>x\<in>s. \<forall>x'\<in>s. dist x' x < d' \<longrightarrow> dist (f x') (f x) < d"
      using `d > 0` using assms(1) unfolding uniformly_continuous_on_def by auto
    then have "\<exists>d>0. \<forall>x\<in>s. \<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist ((g \<circ> f) x') ((g \<circ> f) x) < e"
      using `d>0` using d by auto
  }
  then show ?thesis
    using assms unfolding uniformly_continuous_on_def by auto
qed

text{* Continuity in terms of open preimages. *}

lemma continuous_at_open:
  "continuous (at x) f \<longleftrightarrow> (\<forall>t. open t \<and> f x \<in> t --> (\<exists>s. open s \<and> x \<in> s \<and> (\<forall>x' \<in> s. (f x') \<in> t)))"
  unfolding continuous_within_topological [of x UNIV f]
  unfolding imp_conjL
  by (intro all_cong imp_cong ex_cong conj_cong refl) auto

lemma continuous_imp_tendsto:
  assumes "continuous (at x0) f"
    and "x ----> x0"
  shows "(f \<circ> x) ----> (f x0)"
proof (rule topological_tendstoI)
  fix S
  assume "open S" "f x0 \<in> S"
  then obtain T where T_def: "open T" "x0 \<in> T" "\<forall>x\<in>T. f x \<in> S"
     using assms continuous_at_open by metis
  then have "eventually (\<lambda>n. x n \<in> T) sequentially"
    using assms T_def by (auto simp: tendsto_def)
  then show "eventually (\<lambda>n. (f \<circ> x) n \<in> S) sequentially"
    using T_def by (auto elim!: eventually_elim1)
qed

lemma continuous_on_open:
  "continuous_on s f \<longleftrightarrow>
    (\<forall>t. openin (subtopology euclidean (f ` s)) t \<longrightarrow>
      openin (subtopology euclidean s) {x \<in> s. f x \<in> t})"
  unfolding continuous_on_open_invariant openin_open Int_def vimage_def Int_commute
  by (simp add: imp_ex imageI conj_commute eq_commute cong: conj_cong)

text {* Similarly in terms of closed sets. *}

lemma continuous_on_closed:
  "continuous_on s f \<longleftrightarrow>
    (\<forall>t. closedin (subtopology euclidean (f ` s)) t \<longrightarrow>
      closedin (subtopology euclidean s) {x \<in> s. f x \<in> t})"
  unfolding continuous_on_closed_invariant closedin_closed Int_def vimage_def Int_commute
  by (simp add: imp_ex imageI conj_commute eq_commute cong: conj_cong)

text {* Half-global and completely global cases. *}

lemma continuous_open_in_preimage:
  assumes "continuous_on s f"  "open t"
  shows "openin (subtopology euclidean s) {x \<in> s. f x \<in> t}"
proof -
  have *: "\<forall>x. x \<in> s \<and> f x \<in> t \<longleftrightarrow> x \<in> s \<and> f x \<in> (t \<inter> f ` s)"
    by auto
  have "openin (subtopology euclidean (f ` s)) (t \<inter> f ` s)"
    using openin_open_Int[of t "f ` s", OF assms(2)] unfolding openin_open by auto
  then show ?thesis
    using assms(1)[unfolded continuous_on_open, THEN spec[where x="t \<inter> f ` s"]]
    using * by auto
qed

lemma continuous_closed_in_preimage:
  assumes "continuous_on s f" and "closed t"
  shows "closedin (subtopology euclidean s) {x \<in> s. f x \<in> t}"
proof -
  have *: "\<forall>x. x \<in> s \<and> f x \<in> t \<longleftrightarrow> x \<in> s \<and> f x \<in> (t \<inter> f ` s)"
    by auto
  have "closedin (subtopology euclidean (f ` s)) (t \<inter> f ` s)"
    using closedin_closed_Int[of t "f ` s", OF assms(2)] unfolding Int_commute
    by auto
  then show ?thesis
    using assms(1)[unfolded continuous_on_closed, THEN spec[where x="t \<inter> f ` s"]]
    using * by auto
qed

lemma continuous_open_preimage:
  assumes "continuous_on s f"
    and "open s"
    and "open t"
  shows "open {x \<in> s. f x \<in> t}"
proof-
  obtain T where T: "open T" "{x \<in> s. f x \<in> t} = s \<inter> T"
    using continuous_open_in_preimage[OF assms(1,3)] unfolding openin_open by auto
  then show ?thesis
    using open_Int[of s T, OF assms(2)] by auto
qed

lemma continuous_closed_preimage:
  assumes "continuous_on s f"
    and "closed s"
    and "closed t"
  shows "closed {x \<in> s. f x \<in> t}"
proof-
  obtain T where "closed T" "{x \<in> s. f x \<in> t} = s \<inter> T"
    using continuous_closed_in_preimage[OF assms(1,3)]
    unfolding closedin_closed by auto
  then show ?thesis using closed_Int[of s T, OF assms(2)] by auto
qed

lemma continuous_open_preimage_univ:
  "\<forall>x. continuous (at x) f \<Longrightarrow> open s \<Longrightarrow> open {x. f x \<in> s}"
  using continuous_open_preimage[of UNIV f s] open_UNIV continuous_at_imp_continuous_on by auto

lemma continuous_closed_preimage_univ:
  "(\<forall>x. continuous (at x) f) \<Longrightarrow> closed s \<Longrightarrow> closed {x. f x \<in> s}"
  using continuous_closed_preimage[of UNIV f s] closed_UNIV continuous_at_imp_continuous_on by auto

lemma continuous_open_vimage: "\<forall>x. continuous (at x) f \<Longrightarrow> open s \<Longrightarrow> open (f -` s)"
  unfolding vimage_def by (rule continuous_open_preimage_univ)

lemma continuous_closed_vimage: "\<forall>x. continuous (at x) f \<Longrightarrow> closed s \<Longrightarrow> closed (f -` s)"
  unfolding vimage_def by (rule continuous_closed_preimage_univ)

lemma interior_image_subset:
  assumes "\<forall>x. continuous (at x) f"
    and "inj f"
  shows "interior (f ` s) \<subseteq> f ` (interior s)"
proof
  fix x assume "x \<in> interior (f ` s)"
  then obtain T where as: "open T" "x \<in> T" "T \<subseteq> f ` s" ..
  then have "x \<in> f ` s" by auto
  then obtain y where y: "y \<in> s" "x = f y" by auto
  have "open (vimage f T)"
    using assms(1) `open T` by (rule continuous_open_vimage)
  moreover have "y \<in> vimage f T"
    using `x = f y` `x \<in> T` by simp
  moreover have "vimage f T \<subseteq> s"
    using `T \<subseteq> image f s` `inj f` unfolding inj_on_def subset_eq by auto
  ultimately have "y \<in> interior s" ..
  with `x = f y` show "x \<in> f ` interior s" ..
qed

text {* Equality of continuous functions on closure and related results. *}

lemma continuous_closed_in_preimage_constant:
  fixes f :: "_ \<Rightarrow> 'b::t1_space"
  shows "continuous_on s f \<Longrightarrow> closedin (subtopology euclidean s) {x \<in> s. f x = a}"
  using continuous_closed_in_preimage[of s f "{a}"] by auto

lemma continuous_closed_preimage_constant:
  fixes f :: "_ \<Rightarrow> 'b::t1_space"
  shows "continuous_on s f \<Longrightarrow> closed s \<Longrightarrow> closed {x \<in> s. f x = a}"
  using continuous_closed_preimage[of s f "{a}"] by auto

lemma continuous_constant_on_closure:
  fixes f :: "_ \<Rightarrow> 'b::t1_space"
  assumes "continuous_on (closure s) f"
    and "\<forall>x \<in> s. f x = a"
  shows "\<forall>x \<in> (closure s). f x = a"
    using continuous_closed_preimage_constant[of "closure s" f a]
      assms closure_minimal[of s "{x \<in> closure s. f x = a}"] closure_subset
    unfolding subset_eq
    by auto

lemma image_closure_subset:
  assumes "continuous_on (closure s) f"
    and "closed t"
    and "(f ` s) \<subseteq> t"
  shows "f ` (closure s) \<subseteq> t"
proof -
  have "s \<subseteq> {x \<in> closure s. f x \<in> t}"
    using assms(3) closure_subset by auto
  moreover have "closed {x \<in> closure s. f x \<in> t}"
    using continuous_closed_preimage[OF assms(1)] and assms(2) by auto
  ultimately have "closure s = {x \<in> closure s . f x \<in> t}"
    using closure_minimal[of s "{x \<in> closure s. f x \<in> t}"] by auto
  then show ?thesis by auto
qed

lemma continuous_on_closure_norm_le:
  fixes f :: "'a::metric_space \<Rightarrow> 'b::real_normed_vector"
  assumes "continuous_on (closure s) f"
    and "\<forall>y \<in> s. norm(f y) \<le> b"
    and "x \<in> (closure s)"
  shows "norm (f x) \<le> b"
proof -
  have *: "f ` s \<subseteq> cball 0 b"
    using assms(2)[unfolded mem_cball_0[symmetric]] by auto
  show ?thesis
    using image_closure_subset[OF assms(1) closed_cball[of 0 b] *] assms(3)
    unfolding subset_eq
    apply (erule_tac x="f x" in ballE)
    apply (auto simp add: dist_norm)
    done
qed

text {* Making a continuous function avoid some value in a neighbourhood. *}

lemma continuous_within_avoid:
  fixes f :: "'a::metric_space \<Rightarrow> 'b::t1_space"
  assumes "continuous (at x within s) f"
    and "f x \<noteq> a"
  shows "\<exists>e>0. \<forall>y \<in> s. dist x y < e --> f y \<noteq> a"
proof -
  obtain U where "open U" and "f x \<in> U" and "a \<notin> U"
    using t1_space [OF `f x \<noteq> a`] by fast
  have "(f ---> f x) (at x within s)"
    using assms(1) by (simp add: continuous_within)
  then have "eventually (\<lambda>y. f y \<in> U) (at x within s)"
    using `open U` and `f x \<in> U`
    unfolding tendsto_def by fast
  then have "eventually (\<lambda>y. f y \<noteq> a) (at x within s)"
    using `a \<notin> U` by (fast elim: eventually_mono [rotated])
  then show ?thesis
    using `f x \<noteq> a` by (auto simp: dist_commute zero_less_dist_iff eventually_at)
qed

lemma continuous_at_avoid:
  fixes f :: "'a::metric_space \<Rightarrow> 'b::t1_space"
  assumes "continuous (at x) f"
    and "f x \<noteq> a"
  shows "\<exists>e>0. \<forall>y. dist x y < e \<longrightarrow> f y \<noteq> a"
  using assms continuous_within_avoid[of x UNIV f a] by simp

lemma continuous_on_avoid:
  fixes f :: "'a::metric_space \<Rightarrow> 'b::t1_space"
  assumes "continuous_on s f"
    and "x \<in> s"
    and "f x \<noteq> a"
  shows "\<exists>e>0. \<forall>y \<in> s. dist x y < e \<longrightarrow> f y \<noteq> a"
  using assms(1)[unfolded continuous_on_eq_continuous_within, THEN bspec[where x=x],
    OF assms(2)] continuous_within_avoid[of x s f a]
  using assms(3)
  by auto

lemma continuous_on_open_avoid:
  fixes f :: "'a::metric_space \<Rightarrow> 'b::t1_space"
  assumes "continuous_on s f"
    and "open s"
    and "x \<in> s"
    and "f x \<noteq> a"
  shows "\<exists>e>0. \<forall>y. dist x y < e \<longrightarrow> f y \<noteq> a"
  using assms(1)[unfolded continuous_on_eq_continuous_at[OF assms(2)], THEN bspec[where x=x], OF assms(3)]
  using continuous_at_avoid[of x f a] assms(4)
  by auto

text {* Proving a function is constant by proving open-ness of level set. *}

lemma continuous_levelset_open_in_cases:
  fixes f :: "_ \<Rightarrow> 'b::t1_space"
  shows "connected s \<Longrightarrow> continuous_on s f \<Longrightarrow>
        openin (subtopology euclidean s) {x \<in> s. f x = a}
        \<Longrightarrow> (\<forall>x \<in> s. f x \<noteq> a) \<or> (\<forall>x \<in> s. f x = a)"
  unfolding connected_clopen
  using continuous_closed_in_preimage_constant by auto

lemma continuous_levelset_open_in:
  fixes f :: "_ \<Rightarrow> 'b::t1_space"
  shows "connected s \<Longrightarrow> continuous_on s f \<Longrightarrow>
        openin (subtopology euclidean s) {x \<in> s. f x = a} \<Longrightarrow>
        (\<exists>x \<in> s. f x = a)  \<Longrightarrow> (\<forall>x \<in> s. f x = a)"
  using continuous_levelset_open_in_cases[of s f ]
  by meson

lemma continuous_levelset_open:
  fixes f :: "_ \<Rightarrow> 'b::t1_space"
  assumes "connected s"
    and "continuous_on s f"
    and "open {x \<in> s. f x = a}"
    and "\<exists>x \<in> s.  f x = a"
  shows "\<forall>x \<in> s. f x = a"
  using continuous_levelset_open_in[OF assms(1,2), of a, unfolded openin_open]
  using assms (3,4)
  by fast

text {* Some arithmetical combinations (more to prove). *}

lemma open_scaling[intro]:
  fixes s :: "'a::real_normed_vector set"
  assumes "c \<noteq> 0"
    and "open s"
  shows "open((\<lambda>x. c *\<^sub>R x) ` s)"
proof -
  {
    fix x
    assume "x \<in> s"
    then obtain e where "e>0"
      and e:"\<forall>x'. dist x' x < e \<longrightarrow> x' \<in> s" using assms(2)[unfolded open_dist, THEN bspec[where x=x]]
      by auto
    have "e * abs c > 0"
      using assms(1)[unfolded zero_less_abs_iff[symmetric]]
      using mult_pos_pos[OF `e>0`]
      by auto
    moreover
    {
      fix y
      assume "dist y (c *\<^sub>R x) < e * \<bar>c\<bar>"
      then have "norm ((1 / c) *\<^sub>R y - x) < e"
        unfolding dist_norm
        using norm_scaleR[of c "(1 / c) *\<^sub>R y - x", unfolded scaleR_right_diff_distrib, unfolded scaleR_scaleR] assms(1)
          assms(1)[unfolded zero_less_abs_iff[symmetric]] by (simp del:zero_less_abs_iff)
      then have "y \<in> op *\<^sub>R c ` s"
        using rev_image_eqI[of "(1 / c) *\<^sub>R y" s y "op *\<^sub>R c"]
        using e[THEN spec[where x="(1 / c) *\<^sub>R y"]]
        using assms(1)
        unfolding dist_norm scaleR_scaleR
        by auto
    }
    ultimately have "\<exists>e>0. \<forall>x'. dist x' (c *\<^sub>R x) < e \<longrightarrow> x' \<in> op *\<^sub>R c ` s"
      apply (rule_tac x="e * abs c" in exI)
      apply auto
      done
  }
  then show ?thesis unfolding open_dist by auto
qed

lemma minus_image_eq_vimage:
  fixes A :: "'a::ab_group_add set"
  shows "(\<lambda>x. - x) ` A = (\<lambda>x. - x) -` A"
  by (auto intro!: image_eqI [where f="\<lambda>x. - x"])

lemma open_negations:
  fixes s :: "'a::real_normed_vector set"
  shows "open s \<Longrightarrow> open ((\<lambda>x. - x) ` s)"
  using open_scaling [of "- 1" s] by simp

lemma open_translation:
  fixes s :: "'a::real_normed_vector set"
  assumes "open s"
  shows "open((\<lambda>x. a + x) ` s)"
proof -
  {
    fix x
    have "continuous (at x) (\<lambda>x. x - a)"
      by (intro continuous_diff continuous_at_id continuous_const)
  }
  moreover have "{x. x - a \<in> s} = op + a ` s"
    by force
  ultimately show ?thesis using continuous_open_preimage_univ[of "\<lambda>x. x - a" s]
    using assms by auto
qed

lemma open_affinity:
  fixes s :: "'a::real_normed_vector set"
  assumes "open s"  "c \<noteq> 0"
  shows "open ((\<lambda>x. a + c *\<^sub>R x) ` s)"
proof -
  have *: "(\<lambda>x. a + c *\<^sub>R x) = (\<lambda>x. a + x) \<circ> (\<lambda>x. c *\<^sub>R x)"
    unfolding o_def ..
  have "op + a ` op *\<^sub>R c ` s = (op + a \<circ> op *\<^sub>R c) ` s"
    by auto
  then show ?thesis
    using assms open_translation[of "op *\<^sub>R c ` s" a]
    unfolding *
    by auto
qed

lemma interior_translation:
  fixes s :: "'a::real_normed_vector set"
  shows "interior ((\<lambda>x. a + x) ` s) = (\<lambda>x. a + x) ` (interior s)"
proof (rule set_eqI, rule)
  fix x
  assume "x \<in> interior (op + a ` s)"
  then obtain e where "e > 0" and e: "ball x e \<subseteq> op + a ` s"
    unfolding mem_interior by auto
  then have "ball (x - a) e \<subseteq> s"
    unfolding subset_eq Ball_def mem_ball dist_norm
    apply auto
    apply (erule_tac x="a + xa" in allE)
    unfolding ab_group_add_class.diff_diff_eq[symmetric]
    apply auto
    done
  then show "x \<in> op + a ` interior s"
    unfolding image_iff
    apply (rule_tac x="x - a" in bexI)
    unfolding mem_interior
    using `e > 0`
    apply auto
    done
next
  fix x
  assume "x \<in> op + a ` interior s"
  then obtain y e where "e > 0" and e: "ball y e \<subseteq> s" and y: "x = a + y"
    unfolding image_iff Bex_def mem_interior by auto
  {
    fix z
    have *: "a + y - z = y + a - z" by auto
    assume "z \<in> ball x e"
    then have "z - a \<in> s"
      using e[unfolded subset_eq, THEN bspec[where x="z - a"]]
      unfolding mem_ball dist_norm y group_add_class.diff_diff_eq2 *
      by auto
    then have "z \<in> op + a ` s"
      unfolding image_iff by (auto intro!: bexI[where x="z - a"])
  }
  then have "ball x e \<subseteq> op + a ` s"
    unfolding subset_eq by auto
  then show "x \<in> interior (op + a ` s)"
    unfolding mem_interior using `e > 0` by auto
qed

text {* Topological properties of linear functions. *}

lemma linear_lim_0:
  assumes "bounded_linear f"
  shows "(f ---> 0) (at (0))"
proof -
  interpret f: bounded_linear f by fact
  have "(f ---> f 0) (at 0)"
    using tendsto_ident_at by (rule f.tendsto)
  then show ?thesis unfolding f.zero .
qed

lemma linear_continuous_at:
  assumes "bounded_linear f"
  shows "continuous (at a) f"
  unfolding continuous_at using assms
  apply (rule bounded_linear.tendsto)
  apply (rule tendsto_ident_at)
  done

lemma linear_continuous_within:
  "bounded_linear f \<Longrightarrow> continuous (at x within s) f"
  using continuous_at_imp_continuous_within[of x f s] using linear_continuous_at[of f] by auto

lemma linear_continuous_on:
  "bounded_linear f \<Longrightarrow> continuous_on s f"
  using continuous_at_imp_continuous_on[of s f] using linear_continuous_at[of f] by auto

text {* Also bilinear functions, in composition form. *}

lemma bilinear_continuous_at_compose:
  "continuous (at x) f \<Longrightarrow> continuous (at x) g \<Longrightarrow> bounded_bilinear h \<Longrightarrow>
    continuous (at x) (\<lambda>x. h (f x) (g x))"
  unfolding continuous_at
  using Lim_bilinear[of f "f x" "(at x)" g "g x" h]
  by auto

lemma bilinear_continuous_within_compose:
  "continuous (at x within s) f \<Longrightarrow> continuous (at x within s) g \<Longrightarrow> bounded_bilinear h \<Longrightarrow>
    continuous (at x within s) (\<lambda>x. h (f x) (g x))"
  unfolding continuous_within
  using Lim_bilinear[of f "f x"]
  by auto

lemma bilinear_continuous_on_compose:
  "continuous_on s f \<Longrightarrow> continuous_on s g \<Longrightarrow> bounded_bilinear h \<Longrightarrow>
    continuous_on s (\<lambda>x. h (f x) (g x))"
  unfolding continuous_on_def
  by (fast elim: bounded_bilinear.tendsto)

text {* Preservation of compactness and connectedness under continuous function. *}

lemma compact_eq_openin_cover:
  "compact S \<longleftrightarrow>
    (\<forall>C. (\<forall>c\<in>C. openin (subtopology euclidean S) c) \<and> S \<subseteq> \<Union>C \<longrightarrow>
      (\<exists>D\<subseteq>C. finite D \<and> S \<subseteq> \<Union>D))"
proof safe
  fix C
  assume "compact S" and "\<forall>c\<in>C. openin (subtopology euclidean S) c" and "S \<subseteq> \<Union>C"
  then have "\<forall>c\<in>{T. open T \<and> S \<inter> T \<in> C}. open c" and "S \<subseteq> \<Union>{T. open T \<and> S \<inter> T \<in> C}"
    unfolding openin_open by force+
  with `compact S` obtain D where "D \<subseteq> {T. open T \<and> S \<inter> T \<in> C}" and "finite D" and "S \<subseteq> \<Union>D"
    by (rule compactE)
  then have "image (\<lambda>T. S \<inter> T) D \<subseteq> C \<and> finite (image (\<lambda>T. S \<inter> T) D) \<and> S \<subseteq> \<Union>(image (\<lambda>T. S \<inter> T) D)"
    by auto
  then show "\<exists>D\<subseteq>C. finite D \<and> S \<subseteq> \<Union>D" ..
next
  assume 1: "\<forall>C. (\<forall>c\<in>C. openin (subtopology euclidean S) c) \<and> S \<subseteq> \<Union>C \<longrightarrow>
        (\<exists>D\<subseteq>C. finite D \<and> S \<subseteq> \<Union>D)"
  show "compact S"
  proof (rule compactI)
    fix C
    let ?C = "image (\<lambda>T. S \<inter> T) C"
    assume "\<forall>t\<in>C. open t" and "S \<subseteq> \<Union>C"
    then have "(\<forall>c\<in>?C. openin (subtopology euclidean S) c) \<and> S \<subseteq> \<Union>?C"
      unfolding openin_open by auto
    with 1 obtain D where "D \<subseteq> ?C" and "finite D" and "S \<subseteq> \<Union>D"
      by metis
    let ?D = "inv_into C (\<lambda>T. S \<inter> T) ` D"
    have "?D \<subseteq> C \<and> finite ?D \<and> S \<subseteq> \<Union>?D"
    proof (intro conjI)
      from `D \<subseteq> ?C` show "?D \<subseteq> C"
        by (fast intro: inv_into_into)
      from `finite D` show "finite ?D"
        by (rule finite_imageI)
      from `S \<subseteq> \<Union>D` show "S \<subseteq> \<Union>?D"
        apply (rule subset_trans)
        apply clarsimp
        apply (frule subsetD [OF `D \<subseteq> ?C`, THEN f_inv_into_f])
        apply (erule rev_bexI, fast)
        done
    qed
    then show "\<exists>D\<subseteq>C. finite D \<and> S \<subseteq> \<Union>D" ..
  qed
qed

lemma connected_continuous_image:
  assumes "continuous_on s f"
    and "connected s"
  shows "connected(f ` s)"
proof -
  {
    fix T
    assume as:
      "T \<noteq> {}"
      "T \<noteq> f ` s"
      "openin (subtopology euclidean (f ` s)) T"
      "closedin (subtopology euclidean (f ` s)) T"
    have "{x \<in> s. f x \<in> T} = {} \<or> {x \<in> s. f x \<in> T} = s"
      using assms(1)[unfolded continuous_on_open, THEN spec[where x=T]]
      using assms(1)[unfolded continuous_on_closed, THEN spec[where x=T]]
      using assms(2)[unfolded connected_clopen, THEN spec[where x="{x \<in> s. f x \<in> T}"]] as(3,4) by auto
    then have False using as(1,2)
      using as(4)[unfolded closedin_def topspace_euclidean_subtopology] by auto
  }
  then show ?thesis
    unfolding connected_clopen by auto
qed

text {* Continuity implies uniform continuity on a compact domain. *}

lemma compact_uniformly_continuous:
  assumes f: "continuous_on s f"
    and s: "compact s"
  shows "uniformly_continuous_on s f"
  unfolding uniformly_continuous_on_def
proof (cases, safe)
  fix e :: real
  assume "0 < e" "s \<noteq> {}"
  def [simp]: R \<equiv> "{(y, d). y \<in> s \<and> 0 < d \<and> ball y d \<inter> s \<subseteq> {x \<in> s. f x \<in> ball (f y) (e/2) } }"
  let ?b = "(\<lambda>(y, d). ball y (d/2))"
  have "(\<forall>r\<in>R. open (?b r))" "s \<subseteq> (\<Union>r\<in>R. ?b r)"
  proof safe
    fix y
    assume "y \<in> s"
    from continuous_open_in_preimage[OF f open_ball]
    obtain T where "open T" and T: "{x \<in> s. f x \<in> ball (f y) (e/2)} = T \<inter> s"
      unfolding openin_subtopology open_openin by metis
    then obtain d where "ball y d \<subseteq> T" "0 < d"
      using `0 < e` `y \<in> s` by (auto elim!: openE)
    with T `y \<in> s` show "y \<in> (\<Union>r\<in>R. ?b r)"
      by (intro UN_I[of "(y, d)"]) auto
  qed auto
  with s obtain D where D: "finite D" "D \<subseteq> R" "s \<subseteq> (\<Union>(y, d)\<in>D. ball y (d/2))"
    by (rule compactE_image)
  with `s \<noteq> {}` have [simp]: "\<And>x. x < Min (snd ` D) \<longleftrightarrow> (\<forall>(y, d)\<in>D. x < d)"
    by (subst Min_gr_iff) auto
  show "\<exists>d>0. \<forall>x\<in>s. \<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist (f x') (f x) < e"
  proof (rule, safe)
    fix x x'
    assume in_s: "x' \<in> s" "x \<in> s"
    with D obtain y d where x: "x \<in> ball y (d/2)" "(y, d) \<in> D"
      by blast
    moreover assume "dist x x' < Min (snd`D) / 2"
    ultimately have "dist y x' < d"
      by (intro dist_double[where x=x and d=d]) (auto simp: dist_commute)
    with D x in_s show  "dist (f x) (f x') < e"
      by (intro dist_double[where x="f y" and d=e]) (auto simp: dist_commute subset_eq)
  qed (insert D, auto)
qed auto

text {* A uniformly convergent limit of continuous functions is continuous. *}

lemma continuous_uniform_limit:
  fixes f :: "'a \<Rightarrow> 'b::metric_space \<Rightarrow> 'c::metric_space"
  assumes "\<not> trivial_limit F"
    and "eventually (\<lambda>n. continuous_on s (f n)) F"
    and "\<forall>e>0. eventually (\<lambda>n. \<forall>x\<in>s. dist (f n x) (g x) < e) F"
  shows "continuous_on s g"
proof -
  {
    fix x and e :: real
    assume "x\<in>s" "e>0"
    have "eventually (\<lambda>n. \<forall>x\<in>s. dist (f n x) (g x) < e / 3) F"
      using `e>0` assms(3)[THEN spec[where x="e/3"]] by auto
    from eventually_happens [OF eventually_conj [OF this assms(2)]]
    obtain n where n:"\<forall>x\<in>s. dist (f n x) (g x) < e / 3"  "continuous_on s (f n)"
      using assms(1) by blast
    have "e / 3 > 0" using `e>0` by auto
    then obtain d where "d>0" and d:"\<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist (f n x') (f n x) < e / 3"
      using n(2)[unfolded continuous_on_iff, THEN bspec[where x=x], OF `x\<in>s`, THEN spec[where x="e/3"]] by blast
    {
      fix y
      assume "y \<in> s" and "dist y x < d"
      then have "dist (f n y) (f n x) < e / 3"
        by (rule d [rule_format])
      then have "dist (f n y) (g x) < 2 * e / 3"
        using dist_triangle [of "f n y" "g x" "f n x"]
        using n(1)[THEN bspec[where x=x], OF `x\<in>s`]
        by auto
      then have "dist (g y) (g x) < e"
        using n(1)[THEN bspec[where x=y], OF `y\<in>s`]
        using dist_triangle3 [of "g y" "g x" "f n y"]
        by auto
    }
    then have "\<exists>d>0. \<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist (g x') (g x) < e"
      using `d>0` by auto
  }
  then show ?thesis
    unfolding continuous_on_iff by auto
qed


subsection {* Topological stuff lifted from and dropped to R *}

lemma open_real:
  fixes s :: "real set"
  shows "open s \<longleftrightarrow> (\<forall>x \<in> s. \<exists>e>0. \<forall>x'. abs(x' - x) < e --> x' \<in> s)"
  unfolding open_dist dist_norm by simp

lemma islimpt_approachable_real:
  fixes s :: "real set"
  shows "x islimpt s \<longleftrightarrow> (\<forall>e>0.  \<exists>x'\<in> s. x' \<noteq> x \<and> abs(x' - x) < e)"
  unfolding islimpt_approachable dist_norm by simp

lemma closed_real:
  fixes s :: "real set"
  shows "closed s \<longleftrightarrow> (\<forall>x. (\<forall>e>0.  \<exists>x' \<in> s. x' \<noteq> x \<and> abs(x' - x) < e) \<longrightarrow> x \<in> s)"
  unfolding closed_limpt islimpt_approachable dist_norm by simp

lemma continuous_at_real_range:
  fixes f :: "'a::real_normed_vector \<Rightarrow> real"
  shows "continuous (at x) f \<longleftrightarrow> (\<forall>e>0. \<exists>d>0. \<forall>x'. norm(x' - x) < d --> abs(f x' - f x) < e)"
  unfolding continuous_at
  unfolding Lim_at
  unfolding dist_nz[symmetric]
  unfolding dist_norm
  apply auto
  apply (erule_tac x=e in allE)
  apply auto
  apply (rule_tac x=d in exI)
  apply auto
  apply (erule_tac x=x' in allE)
  apply auto
  apply (erule_tac x=e in allE)
  apply auto
  done

lemma continuous_on_real_range:
  fixes f :: "'a::real_normed_vector \<Rightarrow> real"
  shows "continuous_on s f \<longleftrightarrow>
    (\<forall>x \<in> s. \<forall>e>0. \<exists>d>0. (\<forall>x' \<in> s. norm(x' - x) < d \<longrightarrow> abs(f x' - f x) < e))"
  unfolding continuous_on_iff dist_norm by simp

text {* Hence some handy theorems on distance, diameter etc. of/from a set. *}

lemma distance_attains_sup:
  assumes "compact s" "s \<noteq> {}"
  shows "\<exists>x\<in>s. \<forall>y\<in>s. dist a y \<le> dist a x"
proof (rule continuous_attains_sup [OF assms])
  {
    fix x
    assume "x\<in>s"
    have "(dist a ---> dist a x) (at x within s)"
      by (intro tendsto_dist tendsto_const tendsto_ident_at)
  }
  then show "continuous_on s (dist a)"
    unfolding continuous_on ..
qed

text {* For \emph{minimal} distance, we only need closure, not compactness. *}

lemma distance_attains_inf:
  fixes a :: "'a::heine_borel"
  assumes "closed s"
    and "s \<noteq> {}"
  shows "\<exists>x\<in>s. \<forall>y\<in>s. dist a x \<le> dist a y"
proof -
  from assms(2) obtain b where "b \<in> s" by auto
  let ?B = "s \<inter> cball a (dist b a)"
  have "?B \<noteq> {}" using `b \<in> s`
    by (auto simp add: dist_commute)
  moreover have "continuous_on ?B (dist a)"
    by (auto intro!: continuous_at_imp_continuous_on continuous_dist continuous_at_id continuous_const)
  moreover have "compact ?B"
    by (intro closed_inter_compact `closed s` compact_cball)
  ultimately obtain x where "x \<in> ?B" "\<forall>y\<in>?B. dist a x \<le> dist a y"
    by (metis continuous_attains_inf)
  then show ?thesis by fastforce
qed


subsection {* Pasted sets *}

lemma bounded_Times:
  assumes "bounded s" "bounded t"
  shows "bounded (s \<times> t)"
proof -
  obtain x y a b where "\<forall>z\<in>s. dist x z \<le> a" "\<forall>z\<in>t. dist y z \<le> b"
    using assms [unfolded bounded_def] by auto
  then have "\<forall>z\<in>s \<times> t. dist (x, y) z \<le> sqrt (a\<^sup>2 + b\<^sup>2)"
    by (auto simp add: dist_Pair_Pair real_sqrt_le_mono add_mono power_mono)
  then show ?thesis unfolding bounded_any_center [where a="(x, y)"] by auto
qed

lemma mem_Times_iff: "x \<in> A \<times> B \<longleftrightarrow> fst x \<in> A \<and> snd x \<in> B"
  by (induct x) simp

lemma seq_compact_Times: "seq_compact s \<Longrightarrow> seq_compact t \<Longrightarrow> seq_compact (s \<times> t)"
  unfolding seq_compact_def
  apply clarify
  apply (drule_tac x="fst \<circ> f" in spec)
  apply (drule mp, simp add: mem_Times_iff)
  apply (clarify, rename_tac l1 r1)
  apply (drule_tac x="snd \<circ> f \<circ> r1" in spec)
  apply (drule mp, simp add: mem_Times_iff)
  apply (clarify, rename_tac l2 r2)
  apply (rule_tac x="(l1, l2)" in rev_bexI, simp)
  apply (rule_tac x="r1 \<circ> r2" in exI)
  apply (rule conjI, simp add: subseq_def)
  apply (drule_tac f=r2 in LIMSEQ_subseq_LIMSEQ, assumption)
  apply (drule (1) tendsto_Pair) back
  apply (simp add: o_def)
  done

lemma compact_Times:
  assumes "compact s" "compact t"
  shows "compact (s \<times> t)"
proof (rule compactI)
  fix C
  assume C: "\<forall>t\<in>C. open t" "s \<times> t \<subseteq> \<Union>C"
  have "\<forall>x\<in>s. \<exists>a. open a \<and> x \<in> a \<and> (\<exists>d\<subseteq>C. finite d \<and> a \<times> t \<subseteq> \<Union>d)"
  proof
    fix x
    assume "x \<in> s"
    have "\<forall>y\<in>t. \<exists>a b c. c \<in> C \<and> open a \<and> open b \<and> x \<in> a \<and> y \<in> b \<and> a \<times> b \<subseteq> c" (is "\<forall>y\<in>t. ?P y")
    proof
      fix y
      assume "y \<in> t"
      with `x \<in> s` C obtain c where "c \<in> C" "(x, y) \<in> c" "open c" by auto
      then show "?P y" by (auto elim!: open_prod_elim)
    qed
    then obtain a b c where b: "\<And>y. y \<in> t \<Longrightarrow> open (b y)"
      and c: "\<And>y. y \<in> t \<Longrightarrow> c y \<in> C \<and> open (a y) \<and> open (b y) \<and> x \<in> a y \<and> y \<in> b y \<and> a y \<times> b y \<subseteq> c y"
      by metis
    then have "\<forall>y\<in>t. open (b y)" "t \<subseteq> (\<Union>y\<in>t. b y)" by auto
    from compactE_image[OF `compact t` this] obtain D where D: "D \<subseteq> t" "finite D" "t \<subseteq> (\<Union>y\<in>D. b y)"
      by auto
    moreover from D c have "(\<Inter>y\<in>D. a y) \<times> t \<subseteq> (\<Union>y\<in>D. c y)"
      by (fastforce simp: subset_eq)
    ultimately show "\<exists>a. open a \<and> x \<in> a \<and> (\<exists>d\<subseteq>C. finite d \<and> a \<times> t \<subseteq> \<Union>d)"
      using c by (intro exI[of _ "c`D"] exI[of _ "\<Inter>(a`D)"] conjI) (auto intro!: open_INT)
  qed
  then obtain a d where a: "\<forall>x\<in>s. open (a x)" "s \<subseteq> (\<Union>x\<in>s. a x)"
    and d: "\<And>x. x \<in> s \<Longrightarrow> d x \<subseteq> C \<and> finite (d x) \<and> a x \<times> t \<subseteq> \<Union>d x"
    unfolding subset_eq UN_iff by metis
  moreover
  from compactE_image[OF `compact s` a]
  obtain e where e: "e \<subseteq> s" "finite e" and s: "s \<subseteq> (\<Union>x\<in>e. a x)"
    by auto
  moreover
  {
    from s have "s \<times> t \<subseteq> (\<Union>x\<in>e. a x \<times> t)"
      by auto
    also have "\<dots> \<subseteq> (\<Union>x\<in>e. \<Union>d x)"
      using d `e \<subseteq> s` by (intro UN_mono) auto
    finally have "s \<times> t \<subseteq> (\<Union>x\<in>e. \<Union>d x)" .
  }
  ultimately show "\<exists>C'\<subseteq>C. finite C' \<and> s \<times> t \<subseteq> \<Union>C'"
    by (intro exI[of _ "(\<Union>x\<in>e. d x)"]) (auto simp add: subset_eq)
qed

text{* Hence some useful properties follow quite easily. *}

lemma compact_scaling:
  fixes s :: "'a::real_normed_vector set"
  assumes "compact s"
  shows "compact ((\<lambda>x. c *\<^sub>R x) ` s)"
proof -
  let ?f = "\<lambda>x. scaleR c x"
  have *: "bounded_linear ?f" by (rule bounded_linear_scaleR_right)
  show ?thesis
    using compact_continuous_image[of s ?f] continuous_at_imp_continuous_on[of s ?f]
    using linear_continuous_at[OF *] assms
    by auto
qed

lemma compact_negations:
  fixes s :: "'a::real_normed_vector set"
  assumes "compact s"
  shows "compact ((\<lambda>x. - x) ` s)"
  using compact_scaling [OF assms, of "- 1"] by auto

lemma compact_sums:
  fixes s t :: "'a::real_normed_vector set"
  assumes "compact s"
    and "compact t"
  shows "compact {x + y | x y. x \<in> s \<and> y \<in> t}"
proof -
  have *: "{x + y | x y. x \<in> s \<and> y \<in> t} = (\<lambda>z. fst z + snd z) ` (s \<times> t)"
    apply auto
    unfolding image_iff
    apply (rule_tac x="(xa, y)" in bexI)
    apply auto
    done
  have "continuous_on (s \<times> t) (\<lambda>z. fst z + snd z)"
    unfolding continuous_on by (rule ballI) (intro tendsto_intros)
  then show ?thesis
    unfolding * using compact_continuous_image compact_Times [OF assms] by auto
qed

lemma compact_differences:
  fixes s t :: "'a::real_normed_vector set"
  assumes "compact s"
    and "compact t"
  shows "compact {x - y | x y. x \<in> s \<and> y \<in> t}"
proof-
  have "{x - y | x y. x\<in>s \<and> y \<in> t} =  {x + y | x y. x \<in> s \<and> y \<in> (uminus ` t)}"
    apply auto
    apply (rule_tac x= xa in exI)
    apply auto
    done
  then show ?thesis
    using compact_sums[OF assms(1) compact_negations[OF assms(2)]] by auto
qed

lemma compact_translation:
  fixes s :: "'a::real_normed_vector set"
  assumes "compact s"
  shows "compact ((\<lambda>x. a + x) ` s)"
proof -
  have "{x + y |x y. x \<in> s \<and> y \<in> {a}} = (\<lambda>x. a + x) ` s"
    by auto
  then show ?thesis
    using compact_sums[OF assms compact_sing[of a]] by auto
qed

lemma compact_affinity:
  fixes s :: "'a::real_normed_vector set"
  assumes "compact s"
  shows "compact ((\<lambda>x. a + c *\<^sub>R x) ` s)"
proof -
  have "op + a ` op *\<^sub>R c ` s = (\<lambda>x. a + c *\<^sub>R x) ` s"
    by auto
  then show ?thesis
    using compact_translation[OF compact_scaling[OF assms], of a c] by auto
qed

text {* Hence we get the following. *}

lemma compact_sup_maxdistance:
  fixes s :: "'a::metric_space set"
  assumes "compact s"
    and "s \<noteq> {}"
  shows "\<exists>x\<in>s. \<exists>y\<in>s. \<forall>u\<in>s. \<forall>v\<in>s. dist u v \<le> dist x y"
proof -
  have "compact (s \<times> s)"
    using `compact s` by (intro compact_Times)
  moreover have "s \<times> s \<noteq> {}"
    using `s \<noteq> {}` by auto
  moreover have "continuous_on (s \<times> s) (\<lambda>x. dist (fst x) (snd x))"
    by (intro continuous_at_imp_continuous_on ballI continuous_intros)
  ultimately show ?thesis
    using continuous_attains_sup[of "s \<times> s" "\<lambda>x. dist (fst x) (snd x)"] by auto
qed

text {* We can state this in terms of diameter of a set. *}

definition diameter :: "'a::metric_space set \<Rightarrow> real" where
  "diameter S = (if S = {} then 0 else SUP (x,y):S\<times>S. dist x y)"

lemma diameter_bounded_bound:
  fixes s :: "'a :: metric_space set"
  assumes s: "bounded s" "x \<in> s" "y \<in> s"
  shows "dist x y \<le> diameter s"
proof -
  from s obtain z d where z: "\<And>x. x \<in> s \<Longrightarrow> dist z x \<le> d"
    unfolding bounded_def by auto
  have "bdd_above (split dist ` (s\<times>s))"
  proof (intro bdd_aboveI, safe)
    fix a b
    assume "a \<in> s" "b \<in> s"
    with z[of a] z[of b] dist_triangle[of a b z]
    show "dist a b \<le> 2 * d"
      by (simp add: dist_commute)
  qed
  moreover have "(x,y) \<in> s\<times>s" using s by auto
  ultimately have "dist x y \<le> (SUP (x,y):s\<times>s. dist x y)"
    by (rule cSUP_upper2) simp
  with `x \<in> s` show ?thesis
    by (auto simp add: diameter_def)
qed

lemma diameter_lower_bounded:
  fixes s :: "'a :: metric_space set"
  assumes s: "bounded s"
    and d: "0 < d" "d < diameter s"
  shows "\<exists>x\<in>s. \<exists>y\<in>s. d < dist x y"
proof (rule ccontr)
  assume contr: "\<not> ?thesis"
  moreover have "s \<noteq> {}"
    using d by (auto simp add: diameter_def)
  ultimately have "diameter s \<le> d"
    by (auto simp: not_less diameter_def intro!: cSUP_least)
  with `d < diameter s` show False by auto
qed

lemma diameter_bounded:
  assumes "bounded s"
  shows "\<forall>x\<in>s. \<forall>y\<in>s. dist x y \<le> diameter s"
    and "\<forall>d>0. d < diameter s \<longrightarrow> (\<exists>x\<in>s. \<exists>y\<in>s. dist x y > d)"
  using diameter_bounded_bound[of s] diameter_lower_bounded[of s] assms
  by auto

lemma diameter_compact_attained:
  assumes "compact s"
    and "s \<noteq> {}"
  shows "\<exists>x\<in>s. \<exists>y\<in>s. dist x y = diameter s"
proof -
  have b: "bounded s" using assms(1)
    by (rule compact_imp_bounded)
  then obtain x y where xys: "x\<in>s" "y\<in>s"
    and xy: "\<forall>u\<in>s. \<forall>v\<in>s. dist u v \<le> dist x y"
    using compact_sup_maxdistance[OF assms] by auto
  then have "diameter s \<le> dist x y"
    unfolding diameter_def
    apply clarsimp
    apply (rule cSUP_least)
    apply fast+
    done
  then show ?thesis
    by (metis b diameter_bounded_bound order_antisym xys)
qed

text {* Related results with closure as the conclusion. *}

lemma closed_scaling:
  fixes s :: "'a::real_normed_vector set"
  assumes "closed s"
  shows "closed ((\<lambda>x. c *\<^sub>R x) ` s)"
proof (cases "c = 0")
  case True then show ?thesis
    by (auto simp add: image_constant_conv)
next
  case False
  from assms have "closed ((\<lambda>x. inverse c *\<^sub>R x) -` s)"
    by (simp add: continuous_closed_vimage)
  also have "(\<lambda>x. inverse c *\<^sub>R x) -` s = (\<lambda>x. c *\<^sub>R x) ` s"
    using `c \<noteq> 0` by (auto elim: image_eqI [rotated])
  finally show ?thesis .
qed

lemma closed_negations:
  fixes s :: "'a::real_normed_vector set"
  assumes "closed s"
  shows "closed ((\<lambda>x. -x) ` s)"
  using closed_scaling[OF assms, of "- 1"] by simp

lemma compact_closed_sums:
  fixes s :: "'a::real_normed_vector set"
  assumes "compact s" and "closed t"
  shows "closed {x + y | x y. x \<in> s \<and> y \<in> t}"
proof -
  let ?S = "{x + y |x y. x \<in> s \<and> y \<in> t}"
  {
    fix x l
    assume as: "\<forall>n. x n \<in> ?S"  "(x ---> l) sequentially"
    from as(1) obtain f where f: "\<forall>n. x n = fst (f n) + snd (f n)"  "\<forall>n. fst (f n) \<in> s"  "\<forall>n. snd (f n) \<in> t"
      using choice[of "\<lambda>n y. x n = (fst y) + (snd y) \<and> fst y \<in> s \<and> snd y \<in> t"] by auto
    obtain l' r where "l'\<in>s" and r: "subseq r" and lr: "(((\<lambda>n. fst (f n)) \<circ> r) ---> l') sequentially"
      using assms(1)[unfolded compact_def, THEN spec[where x="\<lambda> n. fst (f n)"]] using f(2) by auto
    have "((\<lambda>n. snd (f (r n))) ---> l - l') sequentially"
      using tendsto_diff[OF LIMSEQ_subseq_LIMSEQ[OF as(2) r] lr] and f(1)
      unfolding o_def
      by auto
    then have "l - l' \<in> t"
      using assms(2)[unfolded closed_sequential_limits,
        THEN spec[where x="\<lambda> n. snd (f (r n))"],
        THEN spec[where x="l - l'"]]
      using f(3)
      by auto
    then have "l \<in> ?S"
      using `l' \<in> s`
      apply auto
      apply (rule_tac x=l' in exI)
      apply (rule_tac x="l - l'" in exI)
      apply auto
      done
  }
  then show ?thesis
    unfolding closed_sequential_limits by fast
qed

lemma closed_compact_sums:
  fixes s t :: "'a::real_normed_vector set"
  assumes "closed s"
    and "compact t"
  shows "closed {x + y | x y. x \<in> s \<and> y \<in> t}"
proof -
  have "{x + y |x y. x \<in> t \<and> y \<in> s} = {x + y |x y. x \<in> s \<and> y \<in> t}"
    apply auto
    apply (rule_tac x=y in exI)
    apply auto
    apply (rule_tac x=y in exI)
    apply auto
    done
  then show ?thesis
    using compact_closed_sums[OF assms(2,1)] by simp
qed

lemma compact_closed_differences:
  fixes s t :: "'a::real_normed_vector set"
  assumes "compact s"
    and "closed t"
  shows "closed {x - y | x y. x \<in> s \<and> y \<in> t}"
proof -
  have "{x + y |x y. x \<in> s \<and> y \<in> uminus ` t} =  {x - y |x y. x \<in> s \<and> y \<in> t}"
    apply auto
    apply (rule_tac x=xa in exI)
    apply auto
    apply (rule_tac x=xa in exI)
    apply auto
    done
  then show ?thesis
    using compact_closed_sums[OF assms(1) closed_negations[OF assms(2)]] by auto
qed

lemma closed_compact_differences:
  fixes s t :: "'a::real_normed_vector set"
  assumes "closed s"
    and "compact t"
  shows "closed {x - y | x y. x \<in> s \<and> y \<in> t}"
proof -
  have "{x + y |x y. x \<in> s \<and> y \<in> uminus ` t} = {x - y |x y. x \<in> s \<and> y \<in> t}"
    apply auto
    apply (rule_tac x=xa in exI)
    apply auto
    apply (rule_tac x=xa in exI)
    apply auto
    done
 then show ?thesis
  using closed_compact_sums[OF assms(1) compact_negations[OF assms(2)]] by simp
qed

lemma closed_translation:
  fixes a :: "'a::real_normed_vector"
  assumes "closed s"
  shows "closed ((\<lambda>x. a + x) ` s)"
proof -
  have "{a + y |y. y \<in> s} = (op + a ` s)" by auto
  then show ?thesis
    using compact_closed_sums[OF compact_sing[of a] assms] by auto
qed

lemma translation_Compl:
  fixes a :: "'a::ab_group_add"
  shows "(\<lambda>x. a + x) ` (- t) = - ((\<lambda>x. a + x) ` t)"
  apply (auto simp add: image_iff)
  apply (rule_tac x="x - a" in bexI)
  apply auto
  done

lemma translation_UNIV:
  fixes a :: "'a::ab_group_add"
  shows "range (\<lambda>x. a + x) = UNIV"
  apply (auto simp add: image_iff)
  apply (rule_tac x="x - a" in exI)
  apply auto
  done

lemma translation_diff:
  fixes a :: "'a::ab_group_add"
  shows "(\<lambda>x. a + x) ` (s - t) = ((\<lambda>x. a + x) ` s) - ((\<lambda>x. a + x) ` t)"
  by auto

lemma closure_translation:
  fixes a :: "'a::real_normed_vector"
  shows "closure ((\<lambda>x. a + x) ` s) = (\<lambda>x. a + x) ` (closure s)"
proof -
  have *: "op + a ` (- s) = - op + a ` s"
    apply auto
    unfolding image_iff
    apply (rule_tac x="x - a" in bexI)
    apply auto
    done
  show ?thesis
    unfolding closure_interior translation_Compl
    using interior_translation[of a "- s"]
    unfolding *
    by auto
qed

lemma frontier_translation:
  fixes a :: "'a::real_normed_vector"
  shows "frontier((\<lambda>x. a + x) ` s) = (\<lambda>x. a + x) ` (frontier s)"
  unfolding frontier_def translation_diff interior_translation closure_translation
  by auto


subsection {* Separation between points and sets *}

lemma separate_point_closed:
  fixes s :: "'a::heine_borel set"
  assumes "closed s"
    and "a \<notin> s"
  shows "\<exists>d>0. \<forall>x\<in>s. d \<le> dist a x"
proof (cases "s = {}")
  case True
  then show ?thesis by(auto intro!: exI[where x=1])
next
  case False
  from assms obtain x where "x\<in>s" "\<forall>y\<in>s. dist a x \<le> dist a y"
    using `s \<noteq> {}` distance_attains_inf [of s a] by blast
  with `x\<in>s` show ?thesis using dist_pos_lt[of a x] and`a \<notin> s`
    by blast
qed

lemma separate_compact_closed:
  fixes s t :: "'a::heine_borel set"
  assumes "compact s"
    and t: "closed t" "s \<inter> t = {}"
  shows "\<exists>d>0. \<forall>x\<in>s. \<forall>y\<in>t. d \<le> dist x y"
proof cases
  assume "s \<noteq> {} \<and> t \<noteq> {}"
  then have "s \<noteq> {}" "t \<noteq> {}" by auto
  let ?inf = "\<lambda>x. infdist x t"
  have "continuous_on s ?inf"
    by (auto intro!: continuous_at_imp_continuous_on continuous_infdist continuous_at_id)
  then obtain x where x: "x \<in> s" "\<forall>y\<in>s. ?inf x \<le> ?inf y"
    using continuous_attains_inf[OF `compact s` `s \<noteq> {}`] by auto
  then have "0 < ?inf x"
    using t `t \<noteq> {}` in_closed_iff_infdist_zero by (auto simp: less_le infdist_nonneg)
  moreover have "\<forall>x'\<in>s. \<forall>y\<in>t. ?inf x \<le> dist x' y"
    using x by (auto intro: order_trans infdist_le)
  ultimately show ?thesis by auto
qed (auto intro!: exI[of _ 1])

lemma separate_closed_compact:
  fixes s t :: "'a::heine_borel set"
  assumes "closed s"
    and "compact t"
    and "s \<inter> t = {}"
  shows "\<exists>d>0. \<forall>x\<in>s. \<forall>y\<in>t. d \<le> dist x y"
proof -
  have *: "t \<inter> s = {}"
    using assms(3) by auto
  show ?thesis
    using separate_compact_closed[OF assms(2,1) *]
    apply auto
    apply (rule_tac x=d in exI)
    apply auto
    apply (erule_tac x=y in ballE)
    apply (auto simp add: dist_commute)
    done
qed

subsection {* Intervals *}

lemma open_box: "open (box a b)"
proof -
  have "open (\<Inter>i\<in>Basis. (op \<bullet> i) -` {a \<bullet> i <..< b \<bullet> i})"
    by (auto intro!: continuous_open_vimage continuous_inner continuous_at_id continuous_const)
  also have "(\<Inter>i\<in>Basis. (op \<bullet> i) -` {a \<bullet> i <..< b \<bullet> i}) = box a b"
    by (auto simp add: box_def inner_commute)
  finally show ?thesis .
qed

instance euclidean_space \<subseteq> second_countable_topology
proof
  def a \<equiv> "\<lambda>f :: 'a \<Rightarrow> (real \<times> real). \<Sum>i\<in>Basis. fst (f i) *\<^sub>R i"
  then have a: "\<And>f. (\<Sum>i\<in>Basis. fst (f i) *\<^sub>R i) = a f"
    by simp
  def b \<equiv> "\<lambda>f :: 'a \<Rightarrow> (real \<times> real). \<Sum>i\<in>Basis. snd (f i) *\<^sub>R i"
  then have b: "\<And>f. (\<Sum>i\<in>Basis. snd (f i) *\<^sub>R i) = b f"
    by simp
  def B \<equiv> "(\<lambda>f. box (a f) (b f)) ` (Basis \<rightarrow>\<^sub>E (\<rat> \<times> \<rat>))"

  have "Ball B open" by (simp add: B_def open_box)
  moreover have "(\<forall>A. open A \<longrightarrow> (\<exists>B'\<subseteq>B. \<Union>B' = A))"
  proof safe
    fix A::"'a set"
    assume "open A"
    show "\<exists>B'\<subseteq>B. \<Union>B' = A"
      apply (rule exI[of _ "{b\<in>B. b \<subseteq> A}"])
      apply (subst (3) open_UNION_box[OF `open A`])
      apply (auto simp add: a b B_def)
      done
  qed
  ultimately
  have "topological_basis B"
    unfolding topological_basis_def by blast
  moreover
  have "countable B"
    unfolding B_def
    by (intro countable_image countable_PiE finite_Basis countable_SIGMA countable_rat)
  ultimately show "\<exists>B::'a set set. countable B \<and> open = generate_topology B"
    by (blast intro: topological_basis_imp_subbasis)
qed

instance euclidean_space \<subseteq> polish_space ..


subsection {* Closure of halfspaces and hyperplanes *}

lemma isCont_open_vimage:
  assumes "\<And>x. isCont f x"
    and "open s"
  shows "open (f -` s)"
proof -
  from assms(1) have "continuous_on UNIV f"
    unfolding isCont_def continuous_on_def by simp
  then have "open {x \<in> UNIV. f x \<in> s}"
    using open_UNIV `open s` by (rule continuous_open_preimage)
  then show "open (f -` s)"
    by (simp add: vimage_def)
qed

lemma isCont_closed_vimage:
  assumes "\<And>x. isCont f x"
    and "closed s"
  shows "closed (f -` s)"
  using assms unfolding closed_def vimage_Compl [symmetric]
  by (rule isCont_open_vimage)

lemma open_Collect_less:
  fixes f g :: "'a::t2_space \<Rightarrow> real"
  assumes f: "\<And>x. isCont f x"
    and g: "\<And>x. isCont g x"
  shows "open {x. f x < g x}"
proof -
  have "open ((\<lambda>x. g x - f x) -` {0<..})"
    using isCont_diff [OF g f] open_real_greaterThan
    by (rule isCont_open_vimage)
  also have "((\<lambda>x. g x - f x) -` {0<..}) = {x. f x < g x}"
    by auto
  finally show ?thesis .
qed

lemma closed_Collect_le:
  fixes f g :: "'a::t2_space \<Rightarrow> real"
  assumes f: "\<And>x. isCont f x"
    and g: "\<And>x. isCont g x"
  shows "closed {x. f x \<le> g x}"
proof -
  have "closed ((\<lambda>x. g x - f x) -` {0..})"
    using isCont_diff [OF g f] closed_real_atLeast
    by (rule isCont_closed_vimage)
  also have "((\<lambda>x. g x - f x) -` {0..}) = {x. f x \<le> g x}"
    by auto
  finally show ?thesis .
qed

lemma closed_Collect_eq:
  fixes f g :: "'a::t2_space \<Rightarrow> 'b::t2_space"
  assumes f: "\<And>x. isCont f x"
    and g: "\<And>x. isCont g x"
  shows "closed {x. f x = g x}"
proof -
  have "open {(x::'b, y::'b). x \<noteq> y}"
    unfolding open_prod_def by (auto dest!: hausdorff)
  then have "closed {(x::'b, y::'b). x = y}"
    unfolding closed_def split_def Collect_neg_eq .
  with isCont_Pair [OF f g]
  have "closed ((\<lambda>x. (f x, g x)) -` {(x, y). x = y})"
    by (rule isCont_closed_vimage)
  also have "\<dots> = {x. f x = g x}" by auto
  finally show ?thesis .
qed

lemma continuous_at_inner: "continuous (at x) (inner a)"
  unfolding continuous_at by (intro tendsto_intros)

lemma closed_halfspace_le: "closed {x. inner a x \<le> b}"
  by (simp add: closed_Collect_le)

lemma closed_halfspace_ge: "closed {x. inner a x \<ge> b}"
  by (simp add: closed_Collect_le)

lemma closed_hyperplane: "closed {x. inner a x = b}"
  by (simp add: closed_Collect_eq)

lemma closed_halfspace_component_le: "closed {x::'a::euclidean_space. x\<bullet>i \<le> a}"
  by (simp add: closed_Collect_le)

lemma closed_halfspace_component_ge: "closed {x::'a::euclidean_space. x\<bullet>i \<ge> a}"
  by (simp add: closed_Collect_le)

lemma closed_interval_left:
  fixes b :: "'a::euclidean_space"
  shows "closed {x::'a. \<forall>i\<in>Basis. x\<bullet>i \<le> b\<bullet>i}"
  by (simp add: Collect_ball_eq closed_INT closed_Collect_le)

lemma closed_interval_right:
  fixes a :: "'a::euclidean_space"
  shows "closed {x::'a. \<forall>i\<in>Basis. a\<bullet>i \<le> x\<bullet>i}"
  by (simp add: Collect_ball_eq closed_INT closed_Collect_le)

text {* Openness of halfspaces. *}

lemma open_halfspace_lt: "open {x. inner a x < b}"
  by (simp add: open_Collect_less)

lemma open_halfspace_gt: "open {x. inner a x > b}"
  by (simp add: open_Collect_less)

lemma open_halfspace_component_lt: "open {x::'a::euclidean_space. x\<bullet>i < a}"
  by (simp add: open_Collect_less)

lemma open_halfspace_component_gt: "open {x::'a::euclidean_space. x\<bullet>i > a}"
  by (simp add: open_Collect_less)

text {* This gives a simple derivation of limit component bounds. *}

lemma Lim_component_le:
  fixes f :: "'a \<Rightarrow> 'b::euclidean_space"
  assumes "(f ---> l) net"
    and "\<not> (trivial_limit net)"
    and "eventually (\<lambda>x. f(x)\<bullet>i \<le> b) net"
  shows "l\<bullet>i \<le> b"
  by (rule tendsto_le[OF assms(2) tendsto_const tendsto_inner[OF assms(1) tendsto_const] assms(3)])

lemma Lim_component_ge:
  fixes f :: "'a \<Rightarrow> 'b::euclidean_space"
  assumes "(f ---> l) net"
    and "\<not> (trivial_limit net)"
    and "eventually (\<lambda>x. b \<le> (f x)\<bullet>i) net"
  shows "b \<le> l\<bullet>i"
  by (rule tendsto_le[OF assms(2) tendsto_inner[OF assms(1) tendsto_const] tendsto_const assms(3)])

lemma Lim_component_eq:
  fixes f :: "'a \<Rightarrow> 'b::euclidean_space"
  assumes net: "(f ---> l) net" "\<not> trivial_limit net"
    and ev:"eventually (\<lambda>x. f(x)\<bullet>i = b) net"
  shows "l\<bullet>i = b"
  using ev[unfolded order_eq_iff eventually_conj_iff]
  using Lim_component_ge[OF net, of b i]
  using Lim_component_le[OF net, of i b]
  by auto

text {* Limits relative to a union. *}

lemma eventually_within_Un:
  "eventually P (at x within (s \<union> t)) \<longleftrightarrow>
    eventually P (at x within s) \<and> eventually P (at x within t)"
  unfolding eventually_at_filter
  by (auto elim!: eventually_rev_mp)

lemma Lim_within_union:
 "(f ---> l) (at x within (s \<union> t)) \<longleftrightarrow>
  (f ---> l) (at x within s) \<and> (f ---> l) (at x within t)"
  unfolding tendsto_def
  by (auto simp add: eventually_within_Un)

lemma Lim_topological:
  "(f ---> l) net \<longleftrightarrow>
    trivial_limit net \<or> (\<forall>S. open S \<longrightarrow> l \<in> S \<longrightarrow> eventually (\<lambda>x. f x \<in> S) net)"
  unfolding tendsto_def trivial_limit_eq by auto

text{* Some more convenient intermediate-value theorem formulations. *}

lemma connected_ivt_hyperplane:
  assumes "connected s"
    and "x \<in> s"
    and "y \<in> s"
    and "inner a x \<le> b"
    and "b \<le> inner a y"
  shows "\<exists>z \<in> s. inner a z = b"
proof (rule ccontr)
  assume as:"\<not> (\<exists>z\<in>s. inner a z = b)"
  let ?A = "{x. inner a x < b}"
  let ?B = "{x. inner a x > b}"
  have "open ?A" "open ?B"
    using open_halfspace_lt and open_halfspace_gt by auto
  moreover
  have "?A \<inter> ?B = {}" by auto
  moreover
  have "s \<subseteq> ?A \<union> ?B" using as by auto
  ultimately
  show False
    using assms(1)[unfolded connected_def not_ex,
      THEN spec[where x="?A"], THEN spec[where x="?B"]]
    using assms(2-5)
    by auto
qed

lemma connected_ivt_component:
  fixes x::"'a::euclidean_space"
  shows "connected s \<Longrightarrow>
    x \<in> s \<Longrightarrow> y \<in> s \<Longrightarrow>
    x\<bullet>k \<le> a \<Longrightarrow> a \<le> y\<bullet>k \<Longrightarrow> (\<exists>z\<in>s.  z\<bullet>k = a)"
  using connected_ivt_hyperplane[of s x y "k::'a" a]
  by (auto simp: inner_commute)


subsection {* Homeomorphisms *}

definition "homeomorphism s t f g \<longleftrightarrow>
  (\<forall>x\<in>s. (g(f x) = x)) \<and> (f ` s = t) \<and> continuous_on s f \<and>
  (\<forall>y\<in>t. (f(g y) = y)) \<and> (g ` t = s) \<and> continuous_on t g"

definition homeomorphic :: "'a::topological_space set \<Rightarrow> 'b::topological_space set \<Rightarrow> bool"
    (infixr "homeomorphic" 60)
  where "s homeomorphic t \<equiv> (\<exists>f g. homeomorphism s t f g)"

lemma homeomorphic_refl: "s homeomorphic s"
  unfolding homeomorphic_def
  unfolding homeomorphism_def
  using continuous_on_id
  apply (rule_tac x = "(\<lambda>x. x)" in exI)
  apply (rule_tac x = "(\<lambda>x. x)" in exI)
  apply blast
  done

lemma homeomorphic_sym: "s homeomorphic t \<longleftrightarrow> t homeomorphic s"
  unfolding homeomorphic_def
  unfolding homeomorphism_def
  by blast

lemma homeomorphic_trans:
  assumes "s homeomorphic t"
    and "t homeomorphic u"
  shows "s homeomorphic u"
proof -
  obtain f1 g1 where fg1: "\<forall>x\<in>s. g1 (f1 x) = x"  "f1 ` s = t"
    "continuous_on s f1" "\<forall>y\<in>t. f1 (g1 y) = y" "g1 ` t = s" "continuous_on t g1"
    using assms(1) unfolding homeomorphic_def homeomorphism_def by auto
  obtain f2 g2 where fg2: "\<forall>x\<in>t. g2 (f2 x) = x"  "f2 ` t = u" "continuous_on t f2"
    "\<forall>y\<in>u. f2 (g2 y) = y" "g2 ` u = t" "continuous_on u g2"
    using assms(2) unfolding homeomorphic_def homeomorphism_def by auto
  {
    fix x
    assume "x\<in>s"
    then have "(g1 \<circ> g2) ((f2 \<circ> f1) x) = x"
      using fg1(1)[THEN bspec[where x=x]] and fg2(1)[THEN bspec[where x="f1 x"]] and fg1(2)
      by auto
  }
  moreover have "(f2 \<circ> f1) ` s = u"
    using fg1(2) fg2(2) by auto
  moreover have "continuous_on s (f2 \<circ> f1)"
    using continuous_on_compose[OF fg1(3)] and fg2(3) unfolding fg1(2) by auto
  moreover
  {
    fix y
    assume "y\<in>u"
    then have "(f2 \<circ> f1) ((g1 \<circ> g2) y) = y"
      using fg2(4)[THEN bspec[where x=y]] and fg1(4)[THEN bspec[where x="g2 y"]] and fg2(5)
      by auto
  }
  moreover have "(g1 \<circ> g2) ` u = s" using fg1(5) fg2(5) by auto
  moreover have "continuous_on u (g1 \<circ> g2)"
    using continuous_on_compose[OF fg2(6)] and fg1(6)
    unfolding fg2(5)
    by auto
  ultimately show ?thesis
    unfolding homeomorphic_def homeomorphism_def
    apply (rule_tac x="f2 \<circ> f1" in exI)
    apply (rule_tac x="g1 \<circ> g2" in exI)
    apply auto
    done
qed

lemma homeomorphic_minimal:
  "s homeomorphic t \<longleftrightarrow>
    (\<exists>f g. (\<forall>x\<in>s. f(x) \<in> t \<and> (g(f(x)) = x)) \<and>
           (\<forall>y\<in>t. g(y) \<in> s \<and> (f(g(y)) = y)) \<and>
           continuous_on s f \<and> continuous_on t g)"
  unfolding homeomorphic_def homeomorphism_def
  apply auto
  apply (rule_tac x=f in exI)
  apply (rule_tac x=g in exI)
  apply auto
  apply (rule_tac x=f in exI)
  apply (rule_tac x=g in exI)
  apply auto
  unfolding image_iff
  apply (erule_tac x="g x" in ballE)
  apply (erule_tac x="x" in ballE)
  apply auto
  apply (rule_tac x="g x" in bexI)
  apply auto
  apply (erule_tac x="f x" in ballE)
  apply (erule_tac x="x" in ballE)
  apply auto
  apply (rule_tac x="f x" in bexI)
  apply auto
  done

text {* Relatively weak hypotheses if a set is compact. *}

lemma homeomorphism_compact:
  fixes f :: "'a::topological_space \<Rightarrow> 'b::t2_space"
  assumes "compact s" "continuous_on s f"  "f ` s = t"  "inj_on f s"
  shows "\<exists>g. homeomorphism s t f g"
proof -
  def g \<equiv> "\<lambda>x. SOME y. y\<in>s \<and> f y = x"
  have g: "\<forall>x\<in>s. g (f x) = x"
    using assms(3) assms(4)[unfolded inj_on_def] unfolding g_def by auto
  {
    fix y
    assume "y \<in> t"
    then obtain x where x:"f x = y" "x\<in>s"
      using assms(3) by auto
    then have "g (f x) = x" using g by auto
    then have "f (g y) = y" unfolding x(1)[symmetric] by auto
  }
  then have g':"\<forall>x\<in>t. f (g x) = x" by auto
  moreover
  {
    fix x
    have "x\<in>s \<Longrightarrow> x \<in> g ` t"
      using g[THEN bspec[where x=x]]
      unfolding image_iff
      using assms(3)
      by (auto intro!: bexI[where x="f x"])
    moreover
    {
      assume "x\<in>g ` t"
      then obtain y where y:"y\<in>t" "g y = x" by auto
      then obtain x' where x':"x'\<in>s" "f x' = y"
        using assms(3) by auto
      then have "x \<in> s"
        unfolding g_def
        using someI2[of "\<lambda>b. b\<in>s \<and> f b = y" x' "\<lambda>x. x\<in>s"]
        unfolding y(2)[symmetric] and g_def
        by auto
    }
    ultimately have "x\<in>s \<longleftrightarrow> x \<in> g ` t" ..
  }
  then have "g ` t = s" by auto
  ultimately show ?thesis
    unfolding homeomorphism_def homeomorphic_def
    apply (rule_tac x=g in exI)
    using g and assms(3) and continuous_on_inv[OF assms(2,1), of g, unfolded assms(3)] and assms(2)
    apply auto
    done
qed

lemma homeomorphic_compact:
  fixes f :: "'a::topological_space \<Rightarrow> 'b::t2_space"
  shows "compact s \<Longrightarrow> continuous_on s f \<Longrightarrow> (f ` s = t) \<Longrightarrow> inj_on f s \<Longrightarrow> s homeomorphic t"
  unfolding homeomorphic_def by (metis homeomorphism_compact)

text{* Preservation of topological properties. *}

lemma homeomorphic_compactness: "s homeomorphic t \<Longrightarrow> (compact s \<longleftrightarrow> compact t)"
  unfolding homeomorphic_def homeomorphism_def
  by (metis compact_continuous_image)

text{* Results on translation, scaling etc. *}

lemma homeomorphic_scaling:
  fixes s :: "'a::real_normed_vector set"
  assumes "c \<noteq> 0"
  shows "s homeomorphic ((\<lambda>x. c *\<^sub>R x) ` s)"
  unfolding homeomorphic_minimal
  apply (rule_tac x="\<lambda>x. c *\<^sub>R x" in exI)
  apply (rule_tac x="\<lambda>x. (1 / c) *\<^sub>R x" in exI)
  using assms
  apply (auto simp add: continuous_on_intros)
  done

lemma homeomorphic_translation:
  fixes s :: "'a::real_normed_vector set"
  shows "s homeomorphic ((\<lambda>x. a + x) ` s)"
  unfolding homeomorphic_minimal
  apply (rule_tac x="\<lambda>x. a + x" in exI)
  apply (rule_tac x="\<lambda>x. -a + x" in exI)
  using continuous_on_add [OF continuous_on_const continuous_on_id, of s a]
    continuous_on_add [OF continuous_on_const continuous_on_id, of "plus a ` s" "- a"]
  apply auto
  done

lemma homeomorphic_affinity:
  fixes s :: "'a::real_normed_vector set"
  assumes "c \<noteq> 0"
  shows "s homeomorphic ((\<lambda>x. a + c *\<^sub>R x) ` s)"
proof -
  have *: "op + a ` op *\<^sub>R c ` s = (\<lambda>x. a + c *\<^sub>R x) ` s" by auto
  show ?thesis
    using homeomorphic_trans
    using homeomorphic_scaling[OF assms, of s]
    using homeomorphic_translation[of "(\<lambda>x. c *\<^sub>R x) ` s" a]
    unfolding *
    by auto
qed

lemma homeomorphic_balls:
  fixes a b ::"'a::real_normed_vector"
  assumes "0 < d"  "0 < e"
  shows "(ball a d) homeomorphic  (ball b e)" (is ?th)
    and "(cball a d) homeomorphic (cball b e)" (is ?cth)
proof -
  show ?th unfolding homeomorphic_minimal
    apply(rule_tac x="\<lambda>x. b + (e/d) *\<^sub>R (x - a)" in exI)
    apply(rule_tac x="\<lambda>x. a + (d/e) *\<^sub>R (x - b)" in exI)
    using assms
    apply (auto intro!: continuous_on_intros
      simp: dist_commute dist_norm pos_divide_less_eq mult_strict_left_mono)
    done
  show ?cth unfolding homeomorphic_minimal
    apply(rule_tac x="\<lambda>x. b + (e/d) *\<^sub>R (x - a)" in exI)
    apply(rule_tac x="\<lambda>x. a + (d/e) *\<^sub>R (x - b)" in exI)
    using assms
    apply (auto intro!: continuous_on_intros
      simp: dist_commute dist_norm pos_divide_le_eq mult_strict_left_mono)
    done
qed

text{* "Isometry" (up to constant bounds) of injective linear map etc.           *}

lemma cauchy_isometric:
  fixes x :: "nat \<Rightarrow> 'a::euclidean_space"
  assumes e: "e > 0"
    and s: "subspace s"
    and f: "bounded_linear f"
    and normf: "\<forall>x\<in>s. norm (f x) \<ge> e * norm x"
    and xs: "\<forall>n. x n \<in> s"
    and cf: "Cauchy (f \<circ> x)"
  shows "Cauchy x"
proof -
  interpret f: bounded_linear f by fact
  {
    fix d :: real
    assume "d > 0"
    then obtain N where N:"\<forall>n\<ge>N. norm (f (x n) - f (x N)) < e * d"
      using cf[unfolded cauchy o_def dist_norm, THEN spec[where x="e*d"]]
        and e and mult_pos_pos[of e d]
      by auto
    {
      fix n
      assume "n\<ge>N"
      have "e * norm (x n - x N) \<le> norm (f (x n - x N))"
        using subspace_sub[OF s, of "x n" "x N"]
        using xs[THEN spec[where x=N]] and xs[THEN spec[where x=n]]
        using normf[THEN bspec[where x="x n - x N"]]
        by auto
      also have "norm (f (x n - x N)) < e * d"
        using `N \<le> n` N unfolding f.diff[symmetric] by auto
      finally have "norm (x n - x N) < d" using `e>0` by simp
    }
    then have "\<exists>N. \<forall>n\<ge>N. norm (x n - x N) < d" by auto
  }
  then show ?thesis unfolding cauchy and dist_norm by auto
qed

lemma complete_isometric_image:
  fixes f :: "'a::euclidean_space \<Rightarrow> 'b::euclidean_space"
  assumes "0 < e"
    and s: "subspace s"
    and f: "bounded_linear f"
    and normf: "\<forall>x\<in>s. norm(f x) \<ge> e * norm(x)"
    and cs: "complete s"
  shows "complete (f ` s)"
proof -
  {
    fix g
    assume as:"\<forall>n::nat. g n \<in> f ` s" and cfg:"Cauchy g"
    then obtain x where "\<forall>n. x n \<in> s \<and> g n = f (x n)"
      using choice[of "\<lambda> n xa. xa \<in> s \<and> g n = f xa"]
      by auto
    then have x:"\<forall>n. x n \<in> s"  "\<forall>n. g n = f (x n)"
      by auto
    then have "f \<circ> x = g"
      unfolding fun_eq_iff
      by auto
    then obtain l where "l\<in>s" and l:"(x ---> l) sequentially"
      using cs[unfolded complete_def, THEN spec[where x="x"]]
      using cauchy_isometric[OF `0 < e` s f normf] and cfg and x(1)
      by auto
    then have "\<exists>l\<in>f ` s. (g ---> l) sequentially"
      using linear_continuous_at[OF f, unfolded continuous_at_sequentially, THEN spec[where x=x], of l]
      unfolding `f \<circ> x = g`
      by auto
  }
  then show ?thesis
    unfolding complete_def by auto
qed

lemma injective_imp_isometric:
  fixes f :: "'a::euclidean_space \<Rightarrow> 'b::euclidean_space"
  assumes s: "closed s" "subspace s"
    and f: "bounded_linear f" "\<forall>x\<in>s. f x = 0 \<longrightarrow> x = 0"
  shows "\<exists>e>0. \<forall>x\<in>s. norm (f x) \<ge> e * norm x"
proof (cases "s \<subseteq> {0::'a}")
  case True
  {
    fix x
    assume "x \<in> s"
    then have "x = 0" using True by auto
    then have "norm x \<le> norm (f x)" by auto
  }
  then show ?thesis by (auto intro!: exI[where x=1])
next
  interpret f: bounded_linear f by fact
  case False
  then obtain a where a: "a \<noteq> 0" "a \<in> s"
    by auto
  from False have "s \<noteq> {}"
    by auto
  let ?S = "{f x| x. (x \<in> s \<and> norm x = norm a)}"
  let ?S' = "{x::'a. x\<in>s \<and> norm x = norm a}"
  let ?S'' = "{x::'a. norm x = norm a}"

  have "?S'' = frontier(cball 0 (norm a))"
    unfolding frontier_cball and dist_norm by auto
  then have "compact ?S''"
    using compact_frontier[OF compact_cball, of 0 "norm a"] by auto
  moreover have "?S' = s \<inter> ?S''" by auto
  ultimately have "compact ?S'"
    using closed_inter_compact[of s ?S''] using s(1) by auto
  moreover have *:"f ` ?S' = ?S" by auto
  ultimately have "compact ?S"
    using compact_continuous_image[OF linear_continuous_on[OF f(1)], of ?S'] by auto
  then have "closed ?S" using compact_imp_closed by auto
  moreover have "?S \<noteq> {}" using a by auto
  ultimately obtain b' where "b'\<in>?S" "\<forall>y\<in>?S. norm b' \<le> norm y"
    using distance_attains_inf[of ?S 0] unfolding dist_0_norm by auto
  then obtain b where "b\<in>s"
    and ba: "norm b = norm a"
    and b: "\<forall>x\<in>{x \<in> s. norm x = norm a}. norm (f b) \<le> norm (f x)"
    unfolding *[symmetric] unfolding image_iff by auto

  let ?e = "norm (f b) / norm b"
  have "norm b > 0" using ba and a and norm_ge_zero by auto
  moreover have "norm (f b) > 0"
    using f(2)[THEN bspec[where x=b], OF `b\<in>s`]
    using `norm b >0`
    unfolding zero_less_norm_iff
    by auto
  ultimately have "0 < norm (f b) / norm b"
    by (simp only: divide_pos_pos)
  moreover
  {
    fix x
    assume "x\<in>s"
    then have "norm (f b) / norm b * norm x \<le> norm (f x)"
    proof (cases "x=0")
      case True
      then show "norm (f b) / norm b * norm x \<le> norm (f x)" by auto
    next
      case False
      then have *: "0 < norm a / norm x"
        using `a\<noteq>0`
        unfolding zero_less_norm_iff[symmetric]
        by (simp only: divide_pos_pos)
      have "\<forall>c. \<forall>x\<in>s. c *\<^sub>R x \<in> s"
        using s[unfolded subspace_def] by auto
      then have "(norm a / norm x) *\<^sub>R x \<in> {x \<in> s. norm x = norm a}"
        using `x\<in>s` and `x\<noteq>0` by auto
      then show "norm (f b) / norm b * norm x \<le> norm (f x)"
        using b[THEN bspec[where x="(norm a / norm x) *\<^sub>R x"]]
        unfolding f.scaleR and ba using `x\<noteq>0` `a\<noteq>0`
        by (auto simp add: mult_commute pos_le_divide_eq pos_divide_le_eq)
    qed
  }
  ultimately show ?thesis by auto
qed

lemma closed_injective_image_subspace:
  fixes f :: "'a::euclidean_space \<Rightarrow> 'b::euclidean_space"
  assumes "subspace s" "bounded_linear f" "\<forall>x\<in>s. f x = 0 \<longrightarrow> x = 0" "closed s"
  shows "closed(f ` s)"
proof -
  obtain e where "e > 0" and e: "\<forall>x\<in>s. e * norm x \<le> norm (f x)"
    using injective_imp_isometric[OF assms(4,1,2,3)] by auto
  show ?thesis
    using complete_isometric_image[OF `e>0` assms(1,2) e] and assms(4)
    unfolding complete_eq_closed[symmetric] by auto
qed


subsection {* Some properties of a canonical subspace *}

lemma subspace_substandard:
  "subspace {x::'a::euclidean_space. (\<forall>i\<in>Basis. P i \<longrightarrow> x\<bullet>i = 0)}"
  unfolding subspace_def by (auto simp: inner_add_left)

lemma closed_substandard:
  "closed {x::'a::euclidean_space. \<forall>i\<in>Basis. P i --> x\<bullet>i = 0}" (is "closed ?A")
proof -
  let ?D = "{i\<in>Basis. P i}"
  have "closed (\<Inter>i\<in>?D. {x::'a. x\<bullet>i = 0})"
    by (simp add: closed_INT closed_Collect_eq)
  also have "(\<Inter>i\<in>?D. {x::'a. x\<bullet>i = 0}) = ?A"
    by auto
  finally show "closed ?A" .
qed

lemma dim_substandard:
  assumes d: "d \<subseteq> Basis"
  shows "dim {x::'a::euclidean_space. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x\<bullet>i = 0} = card d" (is "dim ?A = _")
proof (rule dim_unique)
  show "d \<subseteq> ?A"
    using d by (auto simp: inner_Basis)
  show "independent d"
    using independent_mono [OF independent_Basis d] .
  show "?A \<subseteq> span d"
  proof (clarify)
    fix x assume x: "\<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x \<bullet> i = 0"
    have "finite d"
      using finite_subset [OF d finite_Basis] .
    then have "(\<Sum>i\<in>d. (x \<bullet> i) *\<^sub>R i) \<in> span d"
      by (simp add: span_setsum span_clauses)
    also have "(\<Sum>i\<in>d. (x \<bullet> i) *\<^sub>R i) = (\<Sum>i\<in>Basis. (x \<bullet> i) *\<^sub>R i)"
      by (rule setsum_mono_zero_cong_left [OF finite_Basis d]) (auto simp add: x)
    finally show "x \<in> span d"
      unfolding euclidean_representation .
  qed
qed simp

text{* Hence closure and completeness of all subspaces. *}

lemma ex_card:
  assumes "n \<le> card A"
  shows "\<exists>S\<subseteq>A. card S = n"
proof cases
  assume "finite A"
  from ex_bij_betw_nat_finite[OF this] obtain f where f: "bij_betw f {0..<card A} A" ..
  moreover from f `n \<le> card A` have "{..< n} \<subseteq> {..< card A}" "inj_on f {..< n}"
    by (auto simp: bij_betw_def intro: subset_inj_on)
  ultimately have "f ` {..< n} \<subseteq> A" "card (f ` {..< n}) = n"
    by (auto simp: bij_betw_def card_image)
  then show ?thesis by blast
next
  assume "\<not> finite A"
  with `n \<le> card A` show ?thesis by force
qed

lemma closed_subspace:
  fixes s :: "'a::euclidean_space set"
  assumes "subspace s"
  shows "closed s"
proof -
  have "dim s \<le> card (Basis :: 'a set)"
    using dim_subset_UNIV by auto
  with ex_card[OF this] obtain d :: "'a set" where t: "card d = dim s" and d: "d \<subseteq> Basis"
    by auto
  let ?t = "{x::'a. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x\<bullet>i = 0}"
  have "\<exists>f. linear f \<and> f ` {x::'a. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x \<bullet> i = 0} = s \<and>
      inj_on f {x::'a. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x \<bullet> i = 0}"
    using dim_substandard[of d] t d assms
    by (intro subspace_isomorphism[OF subspace_substandard[of "\<lambda>i. i \<notin> d"]]) (auto simp: inner_Basis)
  then obtain f where f:
      "linear f"
      "f ` {x. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x \<bullet> i = 0} = s"
      "inj_on f {x. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x \<bullet> i = 0}"
    by blast
  interpret f: bounded_linear f
    using f unfolding linear_conv_bounded_linear by auto
  {
    fix x
    have "x\<in>?t \<Longrightarrow> f x = 0 \<Longrightarrow> x = 0"
      using f.zero d f(3)[THEN inj_onD, of x 0] by auto
  }
  moreover have "closed ?t" using closed_substandard .
  moreover have "subspace ?t" using subspace_substandard .
  ultimately show ?thesis
    using closed_injective_image_subspace[of ?t f]
    unfolding f(2) using f(1) unfolding linear_conv_bounded_linear by auto
qed

lemma complete_subspace:
  fixes s :: "('a::euclidean_space) set"
  shows "subspace s \<Longrightarrow> complete s"
  using complete_eq_closed closed_subspace by auto

lemma dim_closure:
  fixes s :: "('a::euclidean_space) set"
  shows "dim(closure s) = dim s" (is "?dc = ?d")
proof -
  have "?dc \<le> ?d" using closure_minimal[OF span_inc, of s]
    using closed_subspace[OF subspace_span, of s]
    using dim_subset[of "closure s" "span s"]
    unfolding dim_span
    by auto
  then show ?thesis using dim_subset[OF closure_subset, of s]
    by auto
qed


subsection {* Affine transformations of intervals *}

lemma real_affinity_le:
 "0 < (m::'a::linordered_field) \<Longrightarrow> (m * x + c \<le> y \<longleftrightarrow> x \<le> inverse(m) * y + -(c / m))"
  by (simp add: field_simps inverse_eq_divide)

lemma real_le_affinity:
 "0 < (m::'a::linordered_field) \<Longrightarrow> (y \<le> m * x + c \<longleftrightarrow> inverse(m) * y + -(c / m) \<le> x)"
  by (simp add: field_simps inverse_eq_divide)

lemma real_affinity_lt:
 "0 < (m::'a::linordered_field) \<Longrightarrow> (m * x + c < y \<longleftrightarrow> x < inverse(m) * y + -(c / m))"
  by (simp add: field_simps inverse_eq_divide)

lemma real_lt_affinity:
 "0 < (m::'a::linordered_field) \<Longrightarrow> (y < m * x + c \<longleftrightarrow> inverse(m) * y + -(c / m) < x)"
  by (simp add: field_simps inverse_eq_divide)

lemma real_affinity_eq:
 "(m::'a::linordered_field) \<noteq> 0 \<Longrightarrow> (m * x + c = y \<longleftrightarrow> x = inverse(m) * y + -(c / m))"
  by (simp add: field_simps inverse_eq_divide)

lemma real_eq_affinity:
 "(m::'a::linordered_field) \<noteq> 0 \<Longrightarrow> (y = m * x + c  \<longleftrightarrow> inverse(m) * y + -(c / m) = x)"
  by (simp add: field_simps inverse_eq_divide)


subsection {* Banach fixed point theorem (not really topological...) *}

lemma banach_fix:
  assumes s: "complete s" "s \<noteq> {}"
    and c: "0 \<le> c" "c < 1"
    and f: "(f ` s) \<subseteq> s"
    and lipschitz: "\<forall>x\<in>s. \<forall>y\<in>s. dist (f x) (f y) \<le> c * dist x y"
  shows "\<exists>!x\<in>s. f x = x"
proof -
  have "1 - c > 0" using c by auto

  from s(2) obtain z0 where "z0 \<in> s" by auto
  def z \<equiv> "\<lambda>n. (f ^^ n) z0"
  {
    fix n :: nat
    have "z n \<in> s" unfolding z_def
    proof (induct n)
      case 0
      then show ?case using `z0 \<in> s` by auto
    next
      case Suc
      then show ?case using f by auto qed
  } note z_in_s = this

  def d \<equiv> "dist (z 0) (z 1)"

  have fzn:"\<And>n. f (z n) = z (Suc n)" unfolding z_def by auto
  {
    fix n :: nat
    have "dist (z n) (z (Suc n)) \<le> (c ^ n) * d"
    proof (induct n)
      case 0
      then show ?case
        unfolding d_def by auto
    next
      case (Suc m)
      then have "c * dist (z m) (z (Suc m)) \<le> c ^ Suc m * d"
        using `0 \<le> c`
        using mult_left_mono[of "dist (z m) (z (Suc m))" "c ^ m * d" c]
        by auto
      then show ?case
        using lipschitz[THEN bspec[where x="z m"], OF z_in_s, THEN bspec[where x="z (Suc m)"], OF z_in_s]
        unfolding fzn and mult_le_cancel_left
        by auto
    qed
  } note cf_z = this

  {
    fix n m :: nat
    have "(1 - c) * dist (z m) (z (m+n)) \<le> (c ^ m) * d * (1 - c ^ n)"
    proof (induct n)
      case 0
      show ?case by auto
    next
      case (Suc k)
      have "(1 - c) * dist (z m) (z (m + Suc k)) \<le>
          (1 - c) * (dist (z m) (z (m + k)) + dist (z (m + k)) (z (Suc (m + k))))"
        using dist_triangle and c by (auto simp add: dist_triangle)
      also have "\<dots> \<le> (1 - c) * (dist (z m) (z (m + k)) + c ^ (m + k) * d)"
        using cf_z[of "m + k"] and c by auto
      also have "\<dots> \<le> c ^ m * d * (1 - c ^ k) + (1 - c) * c ^ (m + k) * d"
        using Suc by (auto simp add: field_simps)
      also have "\<dots> = (c ^ m) * (d * (1 - c ^ k) + (1 - c) * c ^ k * d)"
        unfolding power_add by (auto simp add: field_simps)
      also have "\<dots> \<le> (c ^ m) * d * (1 - c ^ Suc k)"
        using c by (auto simp add: field_simps)
      finally show ?case by auto
    qed
  } note cf_z2 = this
  {
    fix e :: real
    assume "e > 0"
    then have "\<exists>N. \<forall>m n. N \<le> m \<and> N \<le> n \<longrightarrow> dist (z m) (z n) < e"
    proof (cases "d = 0")
      case True
      have *: "\<And>x. ((1 - c) * x \<le> 0) = (x \<le> 0)" using `1 - c > 0`
        by (metis mult_zero_left mult_commute real_mult_le_cancel_iff1)
      from True have "\<And>n. z n = z0" using cf_z2[of 0] and c unfolding z_def
        by (simp add: *)
      then show ?thesis using `e>0` by auto
    next
      case False
      then have "d>0" unfolding d_def using zero_le_dist[of "z 0" "z 1"]
        by (metis False d_def less_le)
      then have "0 < e * (1 - c) / d"
        using `e>0` and `1-c>0`
        using divide_pos_pos[of "e * (1 - c)" d] and mult_pos_pos[of e "1 - c"]
        by auto
      then obtain N where N:"c ^ N < e * (1 - c) / d"
        using real_arch_pow_inv[of "e * (1 - c) / d" c] and c by auto
      {
        fix m n::nat
        assume "m>n" and as:"m\<ge>N" "n\<ge>N"
        have *:"c ^ n \<le> c ^ N" using `n\<ge>N` and c
          using power_decreasing[OF `n\<ge>N`, of c] by auto
        have "1 - c ^ (m - n) > 0"
          using c and power_strict_mono[of c 1 "m - n"] using `m>n` by auto
        then have **: "d * (1 - c ^ (m - n)) / (1 - c) > 0"
          using mult_pos_pos[OF `d>0`, of "1 - c ^ (m - n)"]
          using divide_pos_pos[of "d * (1 - c ^ (m - n))" "1 - c"]
          using `0 < 1 - c`
          by auto

        have "dist (z m) (z n) \<le> c ^ n * d * (1 - c ^ (m - n)) / (1 - c)"
          using cf_z2[of n "m - n"] and `m>n`
          unfolding pos_le_divide_eq[OF `1-c>0`]
          by (auto simp add: mult_commute dist_commute)
        also have "\<dots> \<le> c ^ N * d * (1 - c ^ (m - n)) / (1 - c)"
          using mult_right_mono[OF * order_less_imp_le[OF **]]
          unfolding mult_assoc by auto
        also have "\<dots> < (e * (1 - c) / d) * d * (1 - c ^ (m - n)) / (1 - c)"
          using mult_strict_right_mono[OF N **] unfolding mult_assoc by auto
        also have "\<dots> = e * (1 - c ^ (m - n))"
          using c and `d>0` and `1 - c > 0` by auto
        also have "\<dots> \<le> e" using c and `1 - c ^ (m - n) > 0` and `e>0`
          using mult_right_le_one_le[of e "1 - c ^ (m - n)"] by auto
        finally have  "dist (z m) (z n) < e" by auto
      } note * = this
      {
        fix m n :: nat
        assume as: "N \<le> m" "N \<le> n"
        then have "dist (z n) (z m) < e"
        proof (cases "n = m")
          case True
          then show ?thesis using `e>0` by auto
        next
          case False
          then show ?thesis using as and *[of n m] *[of m n]
            unfolding nat_neq_iff by (auto simp add: dist_commute)
        qed
      }
      then show ?thesis by auto
    qed
  }
  then have "Cauchy z"
    unfolding cauchy_def by auto
  then obtain x where "x\<in>s" and x:"(z ---> x) sequentially"
    using s(1)[unfolded compact_def complete_def, THEN spec[where x=z]] and z_in_s by auto

  def e \<equiv> "dist (f x) x"
  have "e = 0"
  proof (rule ccontr)
    assume "e \<noteq> 0"
    then have "e > 0"
      unfolding e_def using zero_le_dist[of "f x" x]
      by (metis dist_eq_0_iff dist_nz e_def)
    then obtain N where N:"\<forall>n\<ge>N. dist (z n) x < e / 2"
      using x[unfolded LIMSEQ_def, THEN spec[where x="e/2"]] by auto
    then have N':"dist (z N) x < e / 2" by auto

    have *: "c * dist (z N) x \<le> dist (z N) x"
      unfolding mult_le_cancel_right2
      using zero_le_dist[of "z N" x] and c
      by (metis dist_eq_0_iff dist_nz order_less_asym less_le)
    have "dist (f (z N)) (f x) \<le> c * dist (z N) x"
      using lipschitz[THEN bspec[where x="z N"], THEN bspec[where x=x]]
      using z_in_s[of N] `x\<in>s`
      using c
      by auto
    also have "\<dots> < e / 2"
      using N' and c using * by auto
    finally show False
      unfolding fzn
      using N[THEN spec[where x="Suc N"]] and dist_triangle_half_r[of "z (Suc N)" "f x" e x]
      unfolding e_def
      by auto
  qed
  then have "f x = x" unfolding e_def by auto
  moreover
  {
    fix y
    assume "f y = y" "y\<in>s"
    then have "dist x y \<le> c * dist x y"
      using lipschitz[THEN bspec[where x=x], THEN bspec[where x=y]]
      using `x\<in>s` and `f x = x`
      by auto
    then have "dist x y = 0"
      unfolding mult_le_cancel_right1
      using c and zero_le_dist[of x y]
      by auto
    then have "y = x" by auto
  }
  ultimately show ?thesis using `x\<in>s` by blast+
qed


subsection {* Edelstein fixed point theorem *}

lemma edelstein_fix:
  fixes s :: "'a::metric_space set"
  assumes s: "compact s" "s \<noteq> {}"
    and gs: "(g ` s) \<subseteq> s"
    and dist: "\<forall>x\<in>s. \<forall>y\<in>s. x \<noteq> y \<longrightarrow> dist (g x) (g y) < dist x y"
  shows "\<exists>!x\<in>s. g x = x"
proof -
  let ?D = "(\<lambda>x. (x, x)) ` s"
  have D: "compact ?D" "?D \<noteq> {}"
    by (rule compact_continuous_image)
       (auto intro!: s continuous_Pair continuous_within_id simp: continuous_on_eq_continuous_within)

  have "\<And>x y e. x \<in> s \<Longrightarrow> y \<in> s \<Longrightarrow> 0 < e \<Longrightarrow> dist y x < e \<Longrightarrow> dist (g y) (g x) < e"
    using dist by fastforce
  then have "continuous_on s g"
    unfolding continuous_on_iff by auto
  then have cont: "continuous_on ?D (\<lambda>x. dist ((g \<circ> fst) x) (snd x))"
    unfolding continuous_on_eq_continuous_within
    by (intro continuous_dist ballI continuous_within_compose)
       (auto intro!:  continuous_fst continuous_snd continuous_within_id simp: image_image)

  obtain a where "a \<in> s" and le: "\<And>x. x \<in> s \<Longrightarrow> dist (g a) a \<le> dist (g x) x"
    using continuous_attains_inf[OF D cont] by auto

  have "g a = a"
  proof (rule ccontr)
    assume "g a \<noteq> a"
    with `a \<in> s` gs have "dist (g (g a)) (g a) < dist (g a) a"
      by (intro dist[rule_format]) auto
    moreover have "dist (g a) a \<le> dist (g (g a)) (g a)"
      using `a \<in> s` gs by (intro le) auto
    ultimately show False by auto
  qed
  moreover have "\<And>x. x \<in> s \<Longrightarrow> g x = x \<Longrightarrow> x = a"
    using dist[THEN bspec[where x=a]] `g a = a` and `a\<in>s` by auto
  ultimately show "\<exists>!x\<in>s. g x = x" using `a \<in> s` by blast
qed

declare tendsto_const [intro] (* FIXME: move *)

no_notation
  eucl_less (infix "<e" 50)

end