theory Affine
imports Linear_Algebra
begin
lemma if_smult: "(if P then x else (y::real)) *\<^sub>R v = (if P then x *\<^sub>R v else y *\<^sub>R v)"
by (fact if_distrib)
lemma sum_delta_notmem:
assumes "x \<notin> s"
shows "sum (\<lambda>y. if (y = x) then P x else Q y) s = sum Q s"
and "sum (\<lambda>y. if (x = y) then P x else Q y) s = sum Q s"
and "sum (\<lambda>y. if (y = x) then P y else Q y) s = sum Q s"
and "sum (\<lambda>y. if (x = y) then P y else Q y) s = sum Q s"
apply (rule_tac [!] sum.cong)
using assms
apply auto
done
lemmas independent_finite = independent_imp_finite
lemma span_substd_basis:
assumes d: "d \<subseteq> Basis"
shows "span d = {x. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x\<bullet>i = 0}"
(is "_ = ?B")
proof -
have "d \<subseteq> ?B"
using d by (auto simp: inner_Basis)
moreover have s: "subspace ?B"
using subspace_substandard[of "\<lambda>i. i \<notin> d"] .
ultimately have "span d \<subseteq> ?B"
using span_mono[of d "?B"] span_eq_iff[of "?B"] by blast
moreover have *: "card d \<le> dim (span d)"
using independent_card_le_dim[of d "span d"] independent_substdbasis[OF assms]
span_superset[of d]
by auto
moreover from * have "dim ?B \<le> dim (span d)"
using dim_substandard[OF assms] by auto
ultimately show ?thesis
using s subspace_dim_equal[of "span d" "?B"] subspace_span[of d] by auto
qed
lemma basis_to_substdbasis_subspace_isomorphism:
fixes B :: "'a::euclidean_space set"
assumes "independent B"
shows "\<exists>f d::'a set. card d = card B \<and> linear f \<and> f ` B = d \<and>
f ` span B = {x. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x \<bullet> i = 0} \<and> inj_on f (span B) \<and> d \<subseteq> Basis"
proof -
have B: "card B = dim B"
using dim_unique[of B B "card B"] assms span_superset[of B] by auto
have "dim B \<le> card (Basis :: 'a set)"
using dim_subset_UNIV[of B] by simp
from ex_card[OF this] obtain d :: "'a set" where d: "d \<subseteq> Basis" and t: "card d = dim B"
by auto
let ?t = "{x::'a::euclidean_space. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x\<bullet>i = 0}"
have "\<exists>f. linear f \<and> f ` B = d \<and> f ` span B = ?t \<and> inj_on f (span B)"
proof (intro basis_to_basis_subspace_isomorphism subspace_span subspace_substandard span_superset)
show "d \<subseteq> {x. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x \<bullet> i = 0}"
using d inner_not_same_Basis by blast
qed (auto simp: span_substd_basis independent_substdbasis dim_substandard d t B assms)
with t \<open>card B = dim B\<close> d show ?thesis by auto
qed
subsection \<open>Affine set and affine hull\<close>
definition\<^marker>\<open>tag important\<close> affine :: "'a::real_vector set \<Rightarrow> bool"
where "affine s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u v. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> s)"
lemma affine_alt: "affine s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u::real. (1 - u) *\<^sub>R x + u *\<^sub>R y \<in> s)"
unfolding affine_def by (metis eq_diff_eq')
lemma affine_empty [iff]: "affine {}"
unfolding affine_def by auto
lemma affine_sing [iff]: "affine {x}"
unfolding affine_alt by (auto simp: scaleR_left_distrib [symmetric])
lemma affine_UNIV [iff]: "affine UNIV"
unfolding affine_def by auto
lemma affine_Inter [intro]: "(\<And>s. s\<in>f \<Longrightarrow> affine s) \<Longrightarrow> affine (\<Inter>f)"
unfolding affine_def by auto
lemma affine_Int[intro]: "affine s \<Longrightarrow> affine t \<Longrightarrow> affine (s \<inter> t)"
unfolding affine_def by auto
lemma affine_scaling: "affine s \<Longrightarrow> affine (image (\<lambda>x. c *\<^sub>R x) s)"
apply (clarsimp simp add: affine_def)
apply (rule_tac x="u *\<^sub>R x + v *\<^sub>R y" in image_eqI)
apply (auto simp: algebra_simps)
done
lemma affine_affine_hull [simp]: "affine(affine hull s)"
unfolding hull_def
using affine_Inter[of "{t. affine t \<and> s \<subseteq> t}"] by auto
lemma affine_hull_eq[simp]: "(affine hull s = s) \<longleftrightarrow> affine s"
by (metis affine_affine_hull hull_same)
lemma affine_hyperplane: "affine {x. a \<bullet> x = b}"
by (simp add: affine_def algebra_simps) (metis distrib_right mult.left_neutral)
subsubsection\<^marker>\<open>tag unimportant\<close> \<open>Some explicit formulations\<close>
text "Formalized by Lars Schewe."
lemma affine:
fixes V::"'a::real_vector set"
shows "affine V \<longleftrightarrow>
(\<forall>S u. finite S \<and> S \<noteq> {} \<and> S \<subseteq> V \<and> sum u S = 1 \<longrightarrow> (\<Sum>x\<in>S. u x *\<^sub>R x) \<in> V)"
proof -
have "u *\<^sub>R x + v *\<^sub>R y \<in> V" if "x \<in> V" "y \<in> V" "u + v = (1::real)"
and *: "\<And>S u. \<lbrakk>finite S; S \<noteq> {}; S \<subseteq> V; sum u S = 1\<rbrakk> \<Longrightarrow> (\<Sum>x\<in>S. u x *\<^sub>R x) \<in> V" for x y u v
proof (cases "x = y")
case True
then show ?thesis
using that by (metis scaleR_add_left scaleR_one)
next
case False
then show ?thesis
using that *[of "{x,y}" "\<lambda>w. if w = x then u else v"] by auto
qed
moreover have "(\<Sum>x\<in>S. u x *\<^sub>R x) \<in> V"
if *: "\<And>x y u v. \<lbrakk>x\<in>V; y\<in>V; u + v = 1\<rbrakk> \<Longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> V"
and "finite S" "S \<noteq> {}" "S \<subseteq> V" "sum u S = 1" for S u
proof -
define n where "n = card S"
consider "card S = 0" | "card S = 1" | "card S = 2" | "card S > 2" by linarith
then show "(\<Sum>x\<in>S. u x *\<^sub>R x) \<in> V"
proof cases
assume "card S = 1"
then obtain a where "S={a}"
by (auto simp: card_Suc_eq)
then show ?thesis
using that by simp
next
assume "card S = 2"
then obtain a b where "S = {a, b}"
by (metis Suc_1 card_1_singletonE card_Suc_eq)
then show ?thesis
using *[of a b] that
by (auto simp: sum_clauses(2))
next
assume "card S > 2"
then show ?thesis using that n_def
proof (induct n arbitrary: u S)
case 0
then show ?case by auto
next
case (Suc n u S)
have "sum u S = card S" if "\<not> (\<exists>x\<in>S. u x \<noteq> 1)"
using that unfolding card_eq_sum by auto
with Suc.prems obtain x where "x \<in> S" and x: "u x \<noteq> 1" by force
have c: "card (S - {x}) = card S - 1"
by (simp add: Suc.prems(3) \<open>x \<in> S\<close>)
have "sum u (S - {x}) = 1 - u x"
by (simp add: Suc.prems sum_diff1 \<open>x \<in> S\<close>)
with x have eq1: "inverse (1 - u x) * sum u (S - {x}) = 1"
by auto
have inV: "(\<Sum>y\<in>S - {x}. (inverse (1 - u x) * u y) *\<^sub>R y) \<in> V"
proof (cases "card (S - {x}) > 2")
case True
then have S: "S - {x} \<noteq> {}" "card (S - {x}) = n"
using Suc.prems c by force+
show ?thesis
proof (rule Suc.hyps)
show "(\<Sum>a\<in>S - {x}. inverse (1 - u x) * u a) = 1"
by (auto simp: eq1 sum_distrib_left[symmetric])
qed (use S Suc.prems True in auto)
next
case False
then have "card (S - {x}) = Suc (Suc 0)"
using Suc.prems c by auto
then obtain a b where ab: "(S - {x}) = {a, b}" "a\<noteq>b"
unfolding card_Suc_eq by auto
then show ?thesis
using eq1 \<open>S \<subseteq> V\<close>
by (auto simp: sum_distrib_left distrib_left intro!: Suc.prems(2)[of a b])
qed
have "u x + (1 - u x) = 1 \<Longrightarrow>
u x *\<^sub>R x + (1 - u x) *\<^sub>R ((\<Sum>y\<in>S - {x}. u y *\<^sub>R y) /\<^sub>R (1 - u x)) \<in> V"
by (rule Suc.prems) (use \<open>x \<in> S\<close> Suc.prems inV in \<open>auto simp: scaleR_right.sum\<close>)
moreover have "(\<Sum>a\<in>S. u a *\<^sub>R a) = u x *\<^sub>R x + (\<Sum>a\<in>S - {x}. u a *\<^sub>R a)"
by (meson Suc.prems(3) sum.remove \<open>x \<in> S\<close>)
ultimately show "(\<Sum>x\<in>S. u x *\<^sub>R x) \<in> V"
by (simp add: x)
qed
qed (use \<open>S\<noteq>{}\<close> \<open>finite S\<close> in auto)
qed
ultimately show ?thesis
unfolding affine_def by meson
qed
lemma affine_hull_explicit:
"affine hull p = {y. \<exists>S u. finite S \<and> S \<noteq> {} \<and> S \<subseteq> p \<and> sum u S = 1 \<and> sum (\<lambda>v. u v *\<^sub>R v) S = y}"
(is "_ = ?rhs")
proof (rule hull_unique)
show "p \<subseteq> ?rhs"
proof (intro subsetI CollectI exI conjI)
show "\<And>x. sum (\<lambda>z. 1) {x} = 1"
by auto
qed auto
show "?rhs \<subseteq> T" if "p \<subseteq> T" "affine T" for T
using that unfolding affine by blast
show "affine ?rhs"
unfolding affine_def
proof clarify
fix u v :: real and sx ux sy uy
assume uv: "u + v = 1"
and x: "finite sx" "sx \<noteq> {}" "sx \<subseteq> p" "sum ux sx = (1::real)"
and y: "finite sy" "sy \<noteq> {}" "sy \<subseteq> p" "sum uy sy = (1::real)"
have **: "(sx \<union> sy) \<inter> sx = sx" "(sx \<union> sy) \<inter> sy = sy"
by auto
show "\<exists>S w. finite S \<and> S \<noteq> {} \<and> S \<subseteq> p \<and>
sum w S = 1 \<and> (\<Sum>v\<in>S. w v *\<^sub>R v) = u *\<^sub>R (\<Sum>v\<in>sx. ux v *\<^sub>R v) + v *\<^sub>R (\<Sum>v\<in>sy. uy v *\<^sub>R v)"
proof (intro exI conjI)
show "finite (sx \<union> sy)"
using x y by auto
show "sum (\<lambda>i. (if i\<in>sx then u * ux i else 0) + (if i\<in>sy then v * uy i else 0)) (sx \<union> sy) = 1"
using x y uv
by (simp add: sum_Un sum.distrib sum.inter_restrict[symmetric] sum_distrib_left [symmetric] **)
have "(\<Sum>i\<in>sx \<union> sy. ((if i \<in> sx then u * ux i else 0) + (if i \<in> sy then v * uy i else 0)) *\<^sub>R i)
= (\<Sum>i\<in>sx. (u * ux i) *\<^sub>R i) + (\<Sum>i\<in>sy. (v * uy i) *\<^sub>R i)"
using x y
unfolding scaleR_left_distrib scaleR_zero_left if_smult
by (simp add: sum_Un sum.distrib sum.inter_restrict[symmetric] **)
also have "\<dots> = u *\<^sub>R (\<Sum>v\<in>sx. ux v *\<^sub>R v) + v *\<^sub>R (\<Sum>v\<in>sy. uy v *\<^sub>R v)"
unfolding scaleR_scaleR[symmetric] scaleR_right.sum [symmetric] by blast
finally show "(\<Sum>i\<in>sx \<union> sy. ((if i \<in> sx then u * ux i else 0) + (if i \<in> sy then v * uy i else 0)) *\<^sub>R i)
= u *\<^sub>R (\<Sum>v\<in>sx. ux v *\<^sub>R v) + v *\<^sub>R (\<Sum>v\<in>sy. uy v *\<^sub>R v)" .
qed (use x y in auto)
qed
qed
lemma affine_hull_finite:
assumes "finite S"
shows "affine hull S = {y. \<exists>u. sum u S = 1 \<and> sum (\<lambda>v. u v *\<^sub>R v) S = y}"
proof -
have *: "\<exists>h. sum h S = 1 \<and> (\<Sum>v\<in>S. h v *\<^sub>R v) = x"
if "F \<subseteq> S" "finite F" "F \<noteq> {}" and sum: "sum u F = 1" and x: "(\<Sum>v\<in>F. u v *\<^sub>R v) = x" for x F u
proof -
have "S \<inter> F = F"
using that by auto
show ?thesis
proof (intro exI conjI)
show "(\<Sum>x\<in>S. if x \<in> F then u x else 0) = 1"
by (metis (mono_tags, lifting) \<open>S \<inter> F = F\<close> assms sum.inter_restrict sum)
show "(\<Sum>v\<in>S. (if v \<in> F then u v else 0) *\<^sub>R v) = x"
by (simp add: if_smult cong: if_cong) (metis (no_types) \<open>S \<inter> F = F\<close> assms sum.inter_restrict x)
qed
qed
show ?thesis
unfolding affine_hull_explicit using assms
by (fastforce dest: *)
qed
subsubsection\<^marker>\<open>tag unimportant\<close> \<open>Stepping theorems and hence small special cases\<close>
lemma affine_hull_empty[simp]: "affine hull {} = {}"
by simp
lemma affine_hull_finite_step:
fixes y :: "'a::real_vector"
shows "finite S \<Longrightarrow>
(\<exists>u. sum u (insert a S) = w \<and> sum (\<lambda>x. u x *\<^sub>R x) (insert a S) = y) \<longleftrightarrow>
(\<exists>v u. sum u S = w - v \<and> sum (\<lambda>x. u x *\<^sub>R x) S = y - v *\<^sub>R a)" (is "_ \<Longrightarrow> ?lhs = ?rhs")
proof -
assume fin: "finite S"
show "?lhs = ?rhs"
proof
assume ?lhs
then obtain u where u: "sum u (insert a S) = w \<and> (\<Sum>x\<in>insert a S. u x *\<^sub>R x) = y"
by auto
show ?rhs
proof (cases "a \<in> S")
case True
then show ?thesis
using u by (simp add: insert_absorb) (metis diff_zero real_vector.scale_zero_left)
next
case False
show ?thesis
by (rule exI [where x="u a"]) (use u fin False in auto)
qed
next
assume ?rhs
then obtain v u where vu: "sum u S = w - v" "(\<Sum>x\<in>S. u x *\<^sub>R x) = y - v *\<^sub>R a"
by auto
have *: "\<And>x M. (if x = a then v else M) *\<^sub>R x = (if x = a then v *\<^sub>R x else M *\<^sub>R x)"
by auto
show ?lhs
proof (cases "a \<in> S")
case True
show ?thesis
by (rule exI [where x="\<lambda>x. (if x=a then v else 0) + u x"])
(simp add: True scaleR_left_distrib sum.distrib sum_clauses fin vu * cong: if_cong)
next
case False
then show ?thesis
apply (rule_tac x="\<lambda>x. if x=a then v else u x" in exI)
apply (simp add: vu sum_clauses(2)[OF fin] *)
by (simp add: sum_delta_notmem(3) vu)
qed
qed
qed
lemma affine_hull_2:
fixes a b :: "'a::real_vector"
shows "affine hull {a,b} = {u *\<^sub>R a + v *\<^sub>R b| u v. (u + v = 1)}"
(is "?lhs = ?rhs")
proof -
have *:
"\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::real)"
"\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::'a)" by auto
have "?lhs = {y. \<exists>u. sum u {a, b} = 1 \<and> (\<Sum>v\<in>{a, b}. u v *\<^sub>R v) = y}"
using affine_hull_finite[of "{a,b}"] by auto
also have "\<dots> = {y. \<exists>v u. u b = 1 - v \<and> u b *\<^sub>R b = y - v *\<^sub>R a}"
by (simp add: affine_hull_finite_step[of "{b}" a])
also have "\<dots> = ?rhs" unfolding * by auto
finally show ?thesis by auto
qed
lemma affine_hull_3:
fixes a b c :: "'a::real_vector"
shows "affine hull {a,b,c} = { u *\<^sub>R a + v *\<^sub>R b + w *\<^sub>R c| u v w. u + v + w = 1}"
proof -
have *:
"\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::real)"
"\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::'a)" by auto
show ?thesis
apply (simp add: affine_hull_finite affine_hull_finite_step)
unfolding *
apply safe
apply (metis add.assoc)
apply (rule_tac x=u in exI, force)
done
qed
lemma mem_affine:
assumes "affine S" "x \<in> S" "y \<in> S" "u + v = 1"
shows "u *\<^sub>R x + v *\<^sub>R y \<in> S"
using assms affine_def[of S] by auto
lemma mem_affine_3:
assumes "affine S" "x \<in> S" "y \<in> S" "z \<in> S" "u + v + w = 1"
shows "u *\<^sub>R x + v *\<^sub>R y + w *\<^sub>R z \<in> S"
proof -
have "u *\<^sub>R x + v *\<^sub>R y + w *\<^sub>R z \<in> affine hull {x, y, z}"
using affine_hull_3[of x y z] assms by auto
moreover
have "affine hull {x, y, z} \<subseteq> affine hull S"
using hull_mono[of "{x, y, z}" "S"] assms by auto
moreover
have "affine hull S = S"
using assms affine_hull_eq[of S] by auto
ultimately show ?thesis by auto
qed
lemma mem_affine_3_minus:
assumes "affine S" "x \<in> S" "y \<in> S" "z \<in> S"
shows "x + v *\<^sub>R (y-z) \<in> S"
using mem_affine_3[of S x y z 1 v "-v"] assms
by (simp add: algebra_simps)
corollary%unimportant mem_affine_3_minus2:
"\<lbrakk>affine S; x \<in> S; y \<in> S; z \<in> S\<rbrakk> \<Longrightarrow> x - v *\<^sub>R (y-z) \<in> S"
by (metis add_uminus_conv_diff mem_affine_3_minus real_vector.scale_minus_left)
subsubsection\<^marker>\<open>tag unimportant\<close> \<open>Some relations between affine hull and subspaces\<close>
lemma affine_hull_insert_subset_span:
"affine hull (insert a S) \<subseteq> {a + v| v . v \<in> span {x - a | x . x \<in> S}}"
proof -
have "\<exists>v T u. x = a + v \<and> (finite T \<and> T \<subseteq> {x - a |x. x \<in> S} \<and> (\<Sum>v\<in>T. u v *\<^sub>R v) = v)"
if "finite F" "F \<noteq> {}" "F \<subseteq> insert a S" "sum u F = 1" "(\<Sum>v\<in>F. u v *\<^sub>R v) = x"
for x F u
proof -
have *: "(\<lambda>x. x - a) ` (F - {a}) \<subseteq> {x - a |x. x \<in> S}"
using that by auto
show ?thesis
proof (intro exI conjI)
show "finite ((\<lambda>x. x - a) ` (F - {a}))"
by (simp add: that(1))
show "(\<Sum>v\<in>(\<lambda>x. x - a) ` (F - {a}). u(v+a) *\<^sub>R v) = x-a"
by (simp add: sum.reindex[unfolded inj_on_def] algebra_simps
sum_subtractf scaleR_left.sum[symmetric] sum_diff1 that)
qed (use \<open>F \<subseteq> insert a S\<close> in auto)
qed
then show ?thesis
unfolding affine_hull_explicit span_explicit by blast
qed
lemma affine_hull_insert_span:
assumes "a \<notin> S"
shows "affine hull (insert a S) = {a + v | v . v \<in> span {x - a | x. x \<in> S}}"
proof -
have *: "\<exists>G u. finite G \<and> G \<noteq> {} \<and> G \<subseteq> insert a S \<and> sum u G = 1 \<and> (\<Sum>v\<in>G. u v *\<^sub>R v) = y"
if "v \<in> span {x - a |x. x \<in> S}" "y = a + v" for y v
proof -
from that
obtain T u where u: "finite T" "T \<subseteq> {x - a |x. x \<in> S}" "a + (\<Sum>v\<in>T. u v *\<^sub>R v) = y"
unfolding span_explicit by auto
define F where "F = (\<lambda>x. x + a) ` T"
have F: "finite F" "F \<subseteq> S" "(\<Sum>v\<in>F. u (v - a) *\<^sub>R (v - a)) = y - a"
unfolding F_def using u by (auto simp: sum.reindex[unfolded inj_on_def])
have *: "F \<inter> {a} = {}" "F \<inter> - {a} = F"
using F assms by auto
show "\<exists>G u. finite G \<and> G \<noteq> {} \<and> G \<subseteq> insert a S \<and> sum u G = 1 \<and> (\<Sum>v\<in>G. u v *\<^sub>R v) = y"
apply (rule_tac x = "insert a F" in exI)
apply (rule_tac x = "\<lambda>x. if x=a then 1 - sum (\<lambda>x. u (x - a)) F else u (x - a)" in exI)
using assms F
apply (auto simp: sum_clauses sum.If_cases if_smult sum_subtractf scaleR_left.sum algebra_simps *)
done
qed
show ?thesis
by (intro subset_antisym affine_hull_insert_subset_span) (auto simp: affine_hull_explicit dest!: *)
qed
lemma affine_hull_span:
assumes "a \<in> S"
shows "affine hull S = {a + v | v. v \<in> span {x - a | x. x \<in> S - {a}}}"
using affine_hull_insert_span[of a "S - {a}", unfolded insert_Diff[OF assms]] by auto
subsubsection\<^marker>\<open>tag unimportant\<close> \<open>Parallel affine sets\<close>
definition affine_parallel :: "'a::real_vector set \<Rightarrow> 'a::real_vector set \<Rightarrow> bool"
where "affine_parallel S T \<longleftrightarrow> (\<exists>a. T = (\<lambda>x. a + x) ` S)"
lemma affine_parallel_expl_aux:
fixes S T :: "'a::real_vector set"
assumes "\<And>x. x \<in> S \<longleftrightarrow> a + x \<in> T"
shows "T = (\<lambda>x. a + x) ` S"
proof -
have "x \<in> ((\<lambda>x. a + x) ` S)" if "x \<in> T" for x
using that
by (simp add: image_iff) (metis add.commute diff_add_cancel assms)
moreover have "T \<ge> (\<lambda>x. a + x) ` S"
using assms by auto
ultimately show ?thesis by auto
qed
lemma affine_parallel_expl: "affine_parallel S T \<longleftrightarrow> (\<exists>a. \<forall>x. x \<in> S \<longleftrightarrow> a + x \<in> T)"
by (auto simp add: affine_parallel_def)
(use affine_parallel_expl_aux [of S _ T] in blast)
lemma affine_parallel_reflex: "affine_parallel S S"
unfolding affine_parallel_def
using image_add_0 by blast
lemma affine_parallel_commut:
assumes "affine_parallel A B"
shows "affine_parallel B A"
proof -
from assms obtain a where B: "B = (\<lambda>x. a + x) ` A"
unfolding affine_parallel_def by auto
have [simp]: "(\<lambda>x. x - a) = plus (- a)" by (simp add: fun_eq_iff)
from B show ?thesis
using translation_galois [of B a A]
unfolding affine_parallel_def by blast
qed
lemma affine_parallel_assoc:
assumes "affine_parallel A B"
and "affine_parallel B C"
shows "affine_parallel A C"
proof -
from assms obtain ab where "B = (\<lambda>x. ab + x) ` A"
unfolding affine_parallel_def by auto
moreover
from assms obtain bc where "C = (\<lambda>x. bc + x) ` B"
unfolding affine_parallel_def by auto
ultimately show ?thesis
using translation_assoc[of bc ab A] unfolding affine_parallel_def by auto
qed
lemma affine_translation_aux:
fixes a :: "'a::real_vector"
assumes "affine ((\<lambda>x. a + x) ` S)"
shows "affine S"
proof -
{
fix x y u v
assume xy: "x \<in> S" "y \<in> S" "(u :: real) + v = 1"
then have "(a + x) \<in> ((\<lambda>x. a + x) ` S)" "(a + y) \<in> ((\<lambda>x. a + x) ` S)"
by auto
then have h1: "u *\<^sub>R (a + x) + v *\<^sub>R (a + y) \<in> (\<lambda>x. a + x) ` S"
using xy assms unfolding affine_def by auto
have "u *\<^sub>R (a + x) + v *\<^sub>R (a + y) = (u + v) *\<^sub>R a + (u *\<^sub>R x + v *\<^sub>R y)"
by (simp add: algebra_simps)
also have "\<dots> = a + (u *\<^sub>R x + v *\<^sub>R y)"
using \<open>u + v = 1\<close> by auto
ultimately have "a + (u *\<^sub>R x + v *\<^sub>R y) \<in> (\<lambda>x. a + x) ` S"
using h1 by auto
then have "u *\<^sub>R x + v *\<^sub>R y \<in> S" by auto
}
then show ?thesis unfolding affine_def by auto
qed
lemma affine_translation:
"affine S \<longleftrightarrow> affine ((+) a ` S)" for a :: "'a::real_vector"
proof
show "affine ((+) a ` S)" if "affine S"
using that translation_assoc [of "- a" a S]
by (auto intro: affine_translation_aux [of "- a" "((+) a ` S)"])
show "affine S" if "affine ((+) a ` S)"
using that by (rule affine_translation_aux)
qed
lemma parallel_is_affine:
fixes S T :: "'a::real_vector set"
assumes "affine S" "affine_parallel S T"
shows "affine T"
proof -
from assms obtain a where "T = (\<lambda>x. a + x) ` S"
unfolding affine_parallel_def by auto
then show ?thesis
using affine_translation assms by auto
qed
lemma subspace_imp_affine: "subspace s \<Longrightarrow> affine s"
unfolding subspace_def affine_def by auto
lemma affine_hull_subset_span: "(affine hull s) \<subseteq> (span s)"
by (metis hull_minimal span_superset subspace_imp_affine subspace_span)
subsubsection\<^marker>\<open>tag unimportant\<close> \<open>Subspace parallel to an affine set\<close>
lemma subspace_affine: "subspace S \<longleftrightarrow> affine S \<and> 0 \<in> S"
proof -
have h0: "subspace S \<Longrightarrow> affine S \<and> 0 \<in> S"
using subspace_imp_affine[of S] subspace_0 by auto
{
assume assm: "affine S \<and> 0 \<in> S"
{
fix c :: real
fix x
assume x: "x \<in> S"
have "c *\<^sub>R x = (1-c) *\<^sub>R 0 + c *\<^sub>R x" by auto
moreover
have "(1 - c) *\<^sub>R 0 + c *\<^sub>R x \<in> S"
using affine_alt[of S] assm x by auto
ultimately have "c *\<^sub>R x \<in> S" by auto
}
then have h1: "\<forall>c. \<forall>x \<in> S. c *\<^sub>R x \<in> S" by auto
{
fix x y
assume xy: "x \<in> S" "y \<in> S"
define u where "u = (1 :: real)/2"
have "(1/2) *\<^sub>R (x+y) = (1/2) *\<^sub>R (x+y)"
by auto
moreover
have "(1/2) *\<^sub>R (x+y)=(1/2) *\<^sub>R x + (1-(1/2)) *\<^sub>R y"
by (simp add: algebra_simps)
moreover
have "(1 - u) *\<^sub>R x + u *\<^sub>R y \<in> S"
using affine_alt[of S] assm xy by auto
ultimately
have "(1/2) *\<^sub>R (x+y) \<in> S"
using u_def by auto
moreover
have "x + y = 2 *\<^sub>R ((1/2) *\<^sub>R (x+y))"
by auto
ultimately
have "x + y \<in> S"
using h1[rule_format, of "(1/2) *\<^sub>R (x+y)" "2"] by auto
}
then have "\<forall>x \<in> S. \<forall>y \<in> S. x + y \<in> S"
by auto
then have "subspace S"
using h1 assm unfolding subspace_def by auto
}
then show ?thesis using h0 by metis
qed
lemma affine_diffs_subspace:
assumes "affine S" "a \<in> S"
shows "subspace ((\<lambda>x. (-a)+x) ` S)"
proof -
have [simp]: "(\<lambda>x. x - a) = plus (- a)" by (simp add: fun_eq_iff)
have "affine ((\<lambda>x. (-a)+x) ` S)"
using affine_translation assms by blast
moreover have "0 \<in> ((\<lambda>x. (-a)+x) ` S)"
using assms exI[of "(\<lambda>x. x\<in>S \<and> -a+x = 0)" a] by auto
ultimately show ?thesis using subspace_affine by auto
qed
lemma affine_diffs_subspace_subtract:
"subspace ((\<lambda>x. x - a) ` S)" if "affine S" "a \<in> S"
using that affine_diffs_subspace [of _ a] by simp
lemma parallel_subspace_explicit:
assumes "affine S"
and "a \<in> S"
assumes "L \<equiv> {y. \<exists>x \<in> S. (-a) + x = y}"
shows "subspace L \<and> affine_parallel S L"
proof -
from assms have "L = plus (- a) ` S" by auto
then have par: "affine_parallel S L"
unfolding affine_parallel_def ..
then have "affine L" using assms parallel_is_affine by auto
moreover have "0 \<in> L"
using assms by auto
ultimately show ?thesis
using subspace_affine par by auto
qed
lemma parallel_subspace_aux:
assumes "subspace A"
and "subspace B"
and "affine_parallel A B"
shows "A \<supseteq> B"
proof -
from assms obtain a where a: "\<forall>x. x \<in> A \<longleftrightarrow> a + x \<in> B"
using affine_parallel_expl[of A B] by auto
then have "-a \<in> A"
using assms subspace_0[of B] by auto
then have "a \<in> A"
using assms subspace_neg[of A "-a"] by auto
then show ?thesis
using assms a unfolding subspace_def by auto
qed
lemma parallel_subspace:
assumes "subspace A"
and "subspace B"
and "affine_parallel A B"
shows "A = B"
proof
show "A \<supseteq> B"
using assms parallel_subspace_aux by auto
show "A \<subseteq> B"
using assms parallel_subspace_aux[of B A] affine_parallel_commut by auto
qed
lemma affine_parallel_subspace:
assumes "affine S" "S \<noteq> {}"
shows "\<exists>!L. subspace L \<and> affine_parallel S L"
proof -
have ex: "\<exists>L. subspace L \<and> affine_parallel S L"
using assms parallel_subspace_explicit by auto
{
fix L1 L2
assume ass: "subspace L1 \<and> affine_parallel S L1" "subspace L2 \<and> affine_parallel S L2"
then have "affine_parallel L1 L2"
using affine_parallel_commut[of S L1] affine_parallel_assoc[of L1 S L2] by auto
then have "L1 = L2"
using ass parallel_subspace by auto
}
then show ?thesis using ex by auto
qed
subsection \<open>Affine Dependence\<close>
text "Formalized by Lars Schewe."
definition\<^marker>\<open>tag important\<close> affine_dependent :: "'a::real_vector set \<Rightarrow> bool"
where "affine_dependent s \<longleftrightarrow> (\<exists>x\<in>s. x \<in> affine hull (s - {x}))"
lemma affine_dependent_imp_dependent: "affine_dependent s \<Longrightarrow> dependent s"
unfolding affine_dependent_def dependent_def
using affine_hull_subset_span by auto
lemma affine_dependent_subset:
"\<lbrakk>affine_dependent s; s \<subseteq> t\<rbrakk> \<Longrightarrow> affine_dependent t"
apply (simp add: affine_dependent_def Bex_def)
apply (blast dest: hull_mono [OF Diff_mono [OF _ subset_refl]])
done
lemma affine_independent_subset:
shows "\<lbrakk>\<not> affine_dependent t; s \<subseteq> t\<rbrakk> \<Longrightarrow> \<not> affine_dependent s"
by (metis affine_dependent_subset)
lemma affine_independent_Diff:
"\<not> affine_dependent s \<Longrightarrow> \<not> affine_dependent(s - t)"
by (meson Diff_subset affine_dependent_subset)
proposition affine_dependent_explicit:
"affine_dependent p \<longleftrightarrow>
(\<exists>S u. finite S \<and> S \<subseteq> p \<and> sum u S = 0 \<and> (\<exists>v\<in>S. u v \<noteq> 0) \<and> sum (\<lambda>v. u v *\<^sub>R v) S = 0)"
proof -
have "\<exists>S u. finite S \<and> S \<subseteq> p \<and> sum u S = 0 \<and> (\<exists>v\<in>S. u v \<noteq> 0) \<and> (\<Sum>w\<in>S. u w *\<^sub>R w) = 0"
if "(\<Sum>w\<in>S. u w *\<^sub>R w) = x" "x \<in> p" "finite S" "S \<noteq> {}" "S \<subseteq> p - {x}" "sum u S = 1" for x S u
proof (intro exI conjI)
have "x \<notin> S"
using that by auto
then show "(\<Sum>v \<in> insert x S. if v = x then - 1 else u v) = 0"
using that by (simp add: sum_delta_notmem)
show "(\<Sum>w \<in> insert x S. (if w = x then - 1 else u w) *\<^sub>R w) = 0"
using that \<open>x \<notin> S\<close> by (simp add: if_smult sum_delta_notmem cong: if_cong)
qed (use that in auto)
moreover have "\<exists>x\<in>p. \<exists>S u. finite S \<and> S \<noteq> {} \<and> S \<subseteq> p - {x} \<and> sum u S = 1 \<and> (\<Sum>v\<in>S. u v *\<^sub>R v) = x"
if "(\<Sum>v\<in>S. u v *\<^sub>R v) = 0" "finite S" "S \<subseteq> p" "sum u S = 0" "v \<in> S" "u v \<noteq> 0" for S u v
proof (intro bexI exI conjI)
have "S \<noteq> {v}"
using that by auto
then show "S - {v} \<noteq> {}"
using that by auto
show "(\<Sum>x \<in> S - {v}. - (1 / u v) * u x) = 1"
unfolding sum_distrib_left[symmetric] sum_diff1[OF \<open>finite S\<close>] by (simp add: that)
show "(\<Sum>x\<in>S - {v}. (- (1 / u v) * u x) *\<^sub>R x) = v"
unfolding sum_distrib_left [symmetric] scaleR_scaleR[symmetric]
scaleR_right.sum [symmetric] sum_diff1[OF \<open>finite S\<close>]
using that by auto
show "S - {v} \<subseteq> p - {v}"
using that by auto
qed (use that in auto)
ultimately show ?thesis
unfolding affine_dependent_def affine_hull_explicit by auto
qed
lemma affine_dependent_explicit_finite:
fixes S :: "'a::real_vector set"
assumes "finite S"
shows "affine_dependent S \<longleftrightarrow>
(\<exists>u. sum u S = 0 \<and> (\<exists>v\<in>S. u v \<noteq> 0) \<and> sum (\<lambda>v. u v *\<^sub>R v) S = 0)"
(is "?lhs = ?rhs")
proof
have *: "\<And>vt u v. (if vt then u v else 0) *\<^sub>R v = (if vt then (u v) *\<^sub>R v else 0::'a)"
by auto
assume ?lhs
then obtain t u v where
"finite t" "t \<subseteq> S" "sum u t = 0" "v\<in>t" "u v \<noteq> 0" "(\<Sum>v\<in>t. u v *\<^sub>R v) = 0"
unfolding affine_dependent_explicit by auto
then show ?rhs
apply (rule_tac x="\<lambda>x. if x\<in>t then u x else 0" in exI)
apply (auto simp: * sum.inter_restrict[OF assms, symmetric] Int_absorb1[OF \<open>t\<subseteq>S\<close>])
done
next
assume ?rhs
then obtain u v where "sum u S = 0" "v\<in>S" "u v \<noteq> 0" "(\<Sum>v\<in>S. u v *\<^sub>R v) = 0"
by auto
then show ?lhs unfolding affine_dependent_explicit
using assms by auto
qed
lemma dependent_imp_affine_dependent:
assumes "dependent {x - a| x . x \<in> s}"
and "a \<notin> s"
shows "affine_dependent (insert a s)"
proof -
from assms(1)[unfolded dependent_explicit] obtain S u v
where obt: "finite S" "S \<subseteq> {x - a |x. x \<in> s}" "v\<in>S" "u v \<noteq> 0" "(\<Sum>v\<in>S. u v *\<^sub>R v) = 0"
by auto
define t where "t = (\<lambda>x. x + a) ` S"
have inj: "inj_on (\<lambda>x. x + a) S"
unfolding inj_on_def by auto
have "0 \<notin> S"
using obt(2) assms(2) unfolding subset_eq by auto
have fin: "finite t" and "t \<subseteq> s"
unfolding t_def using obt(1,2) by auto
then have "finite (insert a t)" and "insert a t \<subseteq> insert a s"
by auto
moreover have *: "\<And>P Q. (\<Sum>x\<in>t. (if x = a then P x else Q x)) = (\<Sum>x\<in>t. Q x)"
apply (rule sum.cong)
using \<open>a\<notin>s\<close> \<open>t\<subseteq>s\<close>
apply auto
done
have "(\<Sum>x\<in>insert a t. if x = a then - (\<Sum>x\<in>t. u (x - a)) else u (x - a)) = 0"
unfolding sum_clauses(2)[OF fin] * using \<open>a\<notin>s\<close> \<open>t\<subseteq>s\<close> by auto
moreover have "\<exists>v\<in>insert a t. (if v = a then - (\<Sum>x\<in>t. u (x - a)) else u (v - a)) \<noteq> 0"
using obt(3,4) \<open>0\<notin>S\<close>
by (rule_tac x="v + a" in bexI) (auto simp: t_def)
moreover have *: "\<And>P Q. (\<Sum>x\<in>t. (if x = a then P x else Q x) *\<^sub>R x) = (\<Sum>x\<in>t. Q x *\<^sub>R x)"
using \<open>a\<notin>s\<close> \<open>t\<subseteq>s\<close> by (auto intro!: sum.cong)
have "(\<Sum>x\<in>t. u (x - a)) *\<^sub>R a = (\<Sum>v\<in>t. u (v - a) *\<^sub>R v)"
unfolding scaleR_left.sum
unfolding t_def and sum.reindex[OF inj] and o_def
using obt(5)
by (auto simp: sum.distrib scaleR_right_distrib)
then have "(\<Sum>v\<in>insert a t. (if v = a then - (\<Sum>x\<in>t. u (x - a)) else u (v - a)) *\<^sub>R v) = 0"
unfolding sum_clauses(2)[OF fin]
using \<open>a\<notin>s\<close> \<open>t\<subseteq>s\<close>
by (auto simp: *)
ultimately show ?thesis
unfolding affine_dependent_explicit
apply (rule_tac x="insert a t" in exI, auto)
done
qed
lemma affine_dependent_biggerset:
fixes s :: "'a::euclidean_space set"
assumes "finite s" "card s \<ge> DIM('a) + 2"
shows "affine_dependent s"
proof -
have "s \<noteq> {}" using assms by auto
then obtain a where "a\<in>s" by auto
have *: "{x - a |x. x \<in> s - {a}} = (\<lambda>x. x - a) ` (s - {a})"
by auto
have "card {x - a |x. x \<in> s - {a}} = card (s - {a})"
unfolding * by (simp add: card_image inj_on_def)
also have "\<dots> > DIM('a)" using assms(2)
unfolding card_Diff_singleton[OF assms(1) \<open>a\<in>s\<close>] by auto
finally show ?thesis
apply (subst insert_Diff[OF \<open>a\<in>s\<close>, symmetric])
apply (rule dependent_imp_affine_dependent)
apply (rule dependent_biggerset, auto)
done
qed
lemma affine_dependent_biggerset_general:
assumes "finite (S :: 'a::euclidean_space set)"
and "card S \<ge> dim S + 2"
shows "affine_dependent S"
proof -
from assms(2) have "S \<noteq> {}" by auto
then obtain a where "a\<in>S" by auto
have *: "{x - a |x. x \<in> S - {a}} = (\<lambda>x. x - a) ` (S - {a})"
by auto
have **: "card {x - a |x. x \<in> S - {a}} = card (S - {a})"
by (metis (no_types, lifting) "*" card_image diff_add_cancel inj_on_def)
have "dim {x - a |x. x \<in> S - {a}} \<le> dim S"
using \<open>a\<in>S\<close> by (auto simp: span_base span_diff intro: subset_le_dim)
also have "\<dots> < dim S + 1" by auto
also have "\<dots> \<le> card (S - {a})"
using assms
using card_Diff_singleton[OF assms(1) \<open>a\<in>S\<close>]
by auto
finally show ?thesis
apply (subst insert_Diff[OF \<open>a\<in>S\<close>, symmetric])
apply (rule dependent_imp_affine_dependent)
apply (rule dependent_biggerset_general)
unfolding **
apply auto
done
qed
subsection\<^marker>\<open>tag unimportant\<close> \<open>Some Properties of Affine Dependent Sets\<close>
lemma affine_independent_0 [simp]: "\<not> affine_dependent {}"
by (simp add: affine_dependent_def)
lemma affine_independent_1 [simp]: "\<not> affine_dependent {a}"
by (simp add: affine_dependent_def)
lemma affine_independent_2 [simp]: "\<not> affine_dependent {a,b}"
by (simp add: affine_dependent_def insert_Diff_if hull_same)
lemma affine_hull_translation: "affine hull ((\<lambda>x. a + x) ` S) = (\<lambda>x. a + x) ` (affine hull S)"
proof -
have "affine ((\<lambda>x. a + x) ` (affine hull S))"
using affine_translation affine_affine_hull by blast
moreover have "(\<lambda>x. a + x) ` S \<subseteq> (\<lambda>x. a + x) ` (affine hull S)"
using hull_subset[of S] by auto
ultimately have h1: "affine hull ((\<lambda>x. a + x) ` S) \<subseteq> (\<lambda>x. a + x) ` (affine hull S)"
by (metis hull_minimal)
have "affine((\<lambda>x. -a + x) ` (affine hull ((\<lambda>x. a + x) ` S)))"
using affine_translation affine_affine_hull by blast
moreover have "(\<lambda>x. -a + x) ` (\<lambda>x. a + x) ` S \<subseteq> (\<lambda>x. -a + x) ` (affine hull ((\<lambda>x. a + x) ` S))"
using hull_subset[of "(\<lambda>x. a + x) ` S"] by auto
moreover have "S = (\<lambda>x. -a + x) ` (\<lambda>x. a + x) ` S"
using translation_assoc[of "-a" a] by auto
ultimately have "(\<lambda>x. -a + x) ` (affine hull ((\<lambda>x. a + x) ` S)) >= (affine hull S)"
by (metis hull_minimal)
then have "affine hull ((\<lambda>x. a + x) ` S) >= (\<lambda>x. a + x) ` (affine hull S)"
by auto
then show ?thesis using h1 by auto
qed
lemma affine_dependent_translation:
assumes "affine_dependent S"
shows "affine_dependent ((\<lambda>x. a + x) ` S)"
proof -
obtain x where x: "x \<in> S \<and> x \<in> affine hull (S - {x})"
using assms affine_dependent_def by auto
have "(+) a ` (S - {x}) = (+) a ` S - {a + x}"
by auto
then have "a + x \<in> affine hull ((\<lambda>x. a + x) ` S - {a + x})"
using affine_hull_translation[of a "S - {x}"] x by auto
moreover have "a + x \<in> (\<lambda>x. a + x) ` S"
using x by auto
ultimately show ?thesis
unfolding affine_dependent_def by auto
qed
lemma affine_dependent_translation_eq:
"affine_dependent S \<longleftrightarrow> affine_dependent ((\<lambda>x. a + x) ` S)"
proof -
{
assume "affine_dependent ((\<lambda>x. a + x) ` S)"
then have "affine_dependent S"
using affine_dependent_translation[of "((\<lambda>x. a + x) ` S)" "-a"] translation_assoc[of "-a" a]
by auto
}
then show ?thesis
using affine_dependent_translation by auto
qed
lemma affine_hull_0_dependent:
assumes "0 \<in> affine hull S"
shows "dependent S"
proof -
obtain s u where s_u: "finite s \<and> s \<noteq> {} \<and> s \<subseteq> S \<and> sum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = 0"
using assms affine_hull_explicit[of S] by auto
then have "\<exists>v\<in>s. u v \<noteq> 0" by auto
then have "finite s \<and> s \<subseteq> S \<and> (\<exists>v\<in>s. u v \<noteq> 0 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = 0)"
using s_u by auto
then show ?thesis
unfolding dependent_explicit[of S] by auto
qed
lemma affine_dependent_imp_dependent2:
assumes "affine_dependent (insert 0 S)"
shows "dependent S"
proof -
obtain x where x: "x \<in> insert 0 S \<and> x \<in> affine hull (insert 0 S - {x})"
using affine_dependent_def[of "(insert 0 S)"] assms by blast
then have "x \<in> span (insert 0 S - {x})"
using affine_hull_subset_span by auto
moreover have "span (insert 0 S - {x}) = span (S - {x})"
using insert_Diff_if[of "0" S "{x}"] span_insert_0[of "S-{x}"] by auto
ultimately have "x \<in> span (S - {x})" by auto
then have "x \<noteq> 0 \<Longrightarrow> dependent S"
using x dependent_def by auto
moreover
{
assume "x = 0"
then have "0 \<in> affine hull S"
using x hull_mono[of "S - {0}" S] by auto
then have "dependent S"
using affine_hull_0_dependent by auto
}
ultimately show ?thesis by auto
qed
lemma affine_dependent_iff_dependent:
assumes "a \<notin> S"
shows "affine_dependent (insert a S) \<longleftrightarrow> dependent ((\<lambda>x. -a + x) ` S)"
proof -
have "((+) (- a) ` S) = {x - a| x . x \<in> S}" by auto
then show ?thesis
using affine_dependent_translation_eq[of "(insert a S)" "-a"]
affine_dependent_imp_dependent2 assms
dependent_imp_affine_dependent[of a S]
by (auto simp del: uminus_add_conv_diff)
qed
lemma affine_dependent_iff_dependent2:
assumes "a \<in> S"
shows "affine_dependent S \<longleftrightarrow> dependent ((\<lambda>x. -a + x) ` (S-{a}))"
proof -
have "insert a (S - {a}) = S"
using assms by auto
then show ?thesis
using assms affine_dependent_iff_dependent[of a "S-{a}"] by auto
qed
lemma affine_hull_insert_span_gen:
"affine hull (insert a s) = (\<lambda>x. a + x) ` span ((\<lambda>x. - a + x) ` s)"
proof -
have h1: "{x - a |x. x \<in> s} = ((\<lambda>x. -a+x) ` s)"
by auto
{
assume "a \<notin> s"
then have ?thesis
using affine_hull_insert_span[of a s] h1 by auto
}
moreover
{
assume a1: "a \<in> s"
have "\<exists>x. x \<in> s \<and> -a+x=0"
apply (rule exI[of _ a])
using a1
apply auto
done
then have "insert 0 ((\<lambda>x. -a+x) ` (s - {a})) = (\<lambda>x. -a+x) ` s"
by auto
then have "span ((\<lambda>x. -a+x) ` (s - {a}))=span ((\<lambda>x. -a+x) ` s)"
using span_insert_0[of "(+) (- a) ` (s - {a})"] by (auto simp del: uminus_add_conv_diff)
moreover have "{x - a |x. x \<in> (s - {a})} = ((\<lambda>x. -a+x) ` (s - {a}))"
by auto
moreover have "insert a (s - {a}) = insert a s"
by auto
ultimately have ?thesis
using affine_hull_insert_span[of "a" "s-{a}"] by auto
}
ultimately show ?thesis by auto
qed
lemma affine_hull_span2:
assumes "a \<in> s"
shows "affine hull s = (\<lambda>x. a+x) ` span ((\<lambda>x. -a+x) ` (s-{a}))"
using affine_hull_insert_span_gen[of a "s - {a}", unfolded insert_Diff[OF assms]]
by auto
lemma affine_hull_span_gen:
assumes "a \<in> affine hull s"
shows "affine hull s = (\<lambda>x. a+x) ` span ((\<lambda>x. -a+x) ` s)"
proof -
have "affine hull (insert a s) = affine hull s"
using hull_redundant[of a affine s] assms by auto
then show ?thesis
using affine_hull_insert_span_gen[of a "s"] by auto
qed
lemma affine_hull_span_0:
assumes "0 \<in> affine hull S"
shows "affine hull S = span S"
using affine_hull_span_gen[of "0" S] assms by auto
lemma extend_to_affine_basis_nonempty:
fixes S V :: "'n::euclidean_space set"
assumes "\<not> affine_dependent S" "S \<subseteq> V" "S \<noteq> {}"
shows "\<exists>T. \<not> affine_dependent T \<and> S \<subseteq> T \<and> T \<subseteq> V \<and> affine hull T = affine hull V"
proof -
obtain a where a: "a \<in> S"
using assms by auto
then have h0: "independent ((\<lambda>x. -a + x) ` (S-{a}))"
using affine_dependent_iff_dependent2 assms by auto
obtain B where B:
"(\<lambda>x. -a+x) ` (S - {a}) \<subseteq> B \<and> B \<subseteq> (\<lambda>x. -a+x) ` V \<and> independent B \<and> (\<lambda>x. -a+x) ` V \<subseteq> span B"
using assms
by (blast intro: maximal_independent_subset_extend[OF _ h0, of "(\<lambda>x. -a + x) ` V"])
define T where "T = (\<lambda>x. a+x) ` insert 0 B"
then have "T = insert a ((\<lambda>x. a+x) ` B)"
by auto
then have "affine hull T = (\<lambda>x. a+x) ` span B"
using affine_hull_insert_span_gen[of a "((\<lambda>x. a+x) ` B)"] translation_assoc[of "-a" a B]
by auto
then have "V \<subseteq> affine hull T"
using B assms translation_inverse_subset[of a V "span B"]
by auto
moreover have "T \<subseteq> V"
using T_def B a assms by auto
ultimately have "affine hull T = affine hull V"
by (metis Int_absorb1 Int_absorb2 hull_hull hull_mono)
moreover have "S \<subseteq> T"
using T_def B translation_inverse_subset[of a "S-{a}" B]
by auto
moreover have "\<not> affine_dependent T"
using T_def affine_dependent_translation_eq[of "insert 0 B"]
affine_dependent_imp_dependent2 B
by auto
ultimately show ?thesis using \<open>T \<subseteq> V\<close> by auto
qed
lemma affine_basis_exists:
fixes V :: "'n::euclidean_space set"
shows "\<exists>B. B \<subseteq> V \<and> \<not> affine_dependent B \<and> affine hull V = affine hull B"
proof (cases "V = {}")
case True
then show ?thesis
using affine_independent_0 by auto
next
case False
then obtain x where "x \<in> V" by auto
then show ?thesis
using affine_dependent_def[of "{x}"] extend_to_affine_basis_nonempty[of "{x}" V]
by auto
qed
proposition extend_to_affine_basis:
fixes S V :: "'n::euclidean_space set"
assumes "\<not> affine_dependent S" "S \<subseteq> V"
obtains T where "\<not> affine_dependent T" "S \<subseteq> T" "T \<subseteq> V" "affine hull T = affine hull V"
proof (cases "S = {}")
case True then show ?thesis
using affine_basis_exists by (metis empty_subsetI that)
next
case False
then show ?thesis by (metis assms extend_to_affine_basis_nonempty that)
qed
subsection \<open>Affine Dimension of a Set\<close>
definition\<^marker>\<open>tag important\<close> aff_dim :: "('a::euclidean_space) set \<Rightarrow> int"
where "aff_dim V =
(SOME d :: int.
\<exists>B. affine hull B = affine hull V \<and> \<not> affine_dependent B \<and> of_nat (card B) = d + 1)"
lemma aff_dim_basis_exists:
fixes V :: "('n::euclidean_space) set"
shows "\<exists>B. affine hull B = affine hull V \<and> \<not> affine_dependent B \<and> of_nat (card B) = aff_dim V + 1"
proof -
obtain B where "\<not> affine_dependent B \<and> affine hull B = affine hull V"
using affine_basis_exists[of V] by auto
then show ?thesis
unfolding aff_dim_def
some_eq_ex[of "\<lambda>d. \<exists>B. affine hull B = affine hull V \<and> \<not> affine_dependent B \<and> of_nat (card B) = d + 1"]
apply auto
apply (rule exI[of _ "int (card B) - (1 :: int)"])
apply (rule exI[of _ "B"], auto)
done
qed
lemma affine_hull_eq_empty [simp]: "affine hull S = {} \<longleftrightarrow> S = {}"
by (metis affine_empty subset_empty subset_hull)
lemma empty_eq_affine_hull[simp]: "{} = affine hull S \<longleftrightarrow> S = {}"
by (metis affine_hull_eq_empty)
lemma aff_dim_parallel_subspace_aux:
fixes B :: "'n::euclidean_space set"
assumes "\<not> affine_dependent B" "a \<in> B"
shows "finite B \<and> ((card B) - 1 = dim (span ((\<lambda>x. -a+x) ` (B-{a}))))"
proof -
have "independent ((\<lambda>x. -a + x) ` (B-{a}))"
using affine_dependent_iff_dependent2 assms by auto
then have fin: "dim (span ((\<lambda>x. -a+x) ` (B-{a}))) = card ((\<lambda>x. -a + x) ` (B-{a}))"
"finite ((\<lambda>x. -a + x) ` (B - {a}))"
using indep_card_eq_dim_span[of "(\<lambda>x. -a+x) ` (B-{a})"] by auto
show ?thesis
proof (cases "(\<lambda>x. -a + x) ` (B - {a}) = {}")
case True
have "B = insert a ((\<lambda>x. a + x) ` (\<lambda>x. -a + x) ` (B - {a}))"
using translation_assoc[of "a" "-a" "(B - {a})"] assms by auto
then have "B = {a}" using True by auto
then show ?thesis using assms fin by auto
next
case False
then have "card ((\<lambda>x. -a + x) ` (B - {a})) > 0"
using fin by auto
moreover have h1: "card ((\<lambda>x. -a + x) ` (B-{a})) = card (B-{a})"
by (rule card_image) (use translate_inj_on in blast)
ultimately have "card (B-{a}) > 0" by auto
then have *: "finite (B - {a})"
using card_gt_0_iff[of "(B - {a})"] by auto
then have "card (B - {a}) = card B - 1"
using card_Diff_singleton assms by auto
with * show ?thesis using fin h1 by auto
qed
qed
lemma aff_dim_parallel_subspace:
fixes V L :: "'n::euclidean_space set"
assumes "V \<noteq> {}"
and "subspace L"
and "affine_parallel (affine hull V) L"
shows "aff_dim V = int (dim L)"
proof -
obtain B where
B: "affine hull B = affine hull V \<and> \<not> affine_dependent B \<and> int (card B) = aff_dim V + 1"
using aff_dim_basis_exists by auto
then have "B \<noteq> {}"
using assms B
by auto
then obtain a where a: "a \<in> B" by auto
define Lb where "Lb = span ((\<lambda>x. -a+x) ` (B-{a}))"
moreover have "affine_parallel (affine hull B) Lb"
using Lb_def B assms affine_hull_span2[of a B] a
affine_parallel_commut[of "Lb" "(affine hull B)"]
unfolding affine_parallel_def
by auto
moreover have "subspace Lb"
using Lb_def subspace_span by auto
moreover have "affine hull B \<noteq> {}"
using assms B by auto
ultimately have "L = Lb"
using assms affine_parallel_subspace[of "affine hull B"] affine_affine_hull[of B] B
by auto
then have "dim L = dim Lb"
by auto
moreover have "card B - 1 = dim Lb" and "finite B"
using Lb_def aff_dim_parallel_subspace_aux a B by auto
ultimately show ?thesis
using B \<open>B \<noteq> {}\<close> card_gt_0_iff[of B] by auto
qed
lemma aff_independent_finite:
fixes B :: "'n::euclidean_space set"
assumes "\<not> affine_dependent B"
shows "finite B"
proof -
{
assume "B \<noteq> {}"
then obtain a where "a \<in> B" by auto
then have ?thesis
using aff_dim_parallel_subspace_aux assms by auto
}
then show ?thesis by auto
qed
lemma aff_dim_empty:
fixes S :: "'n::euclidean_space set"
shows "S = {} \<longleftrightarrow> aff_dim S = -1"
proof -
obtain B where *: "affine hull B = affine hull S"
and "\<not> affine_dependent B"
and "int (card B) = aff_dim S + 1"
using aff_dim_basis_exists by auto
moreover
from * have "S = {} \<longleftrightarrow> B = {}"
by auto
ultimately show ?thesis
using aff_independent_finite[of B] card_gt_0_iff[of B] by auto
qed
lemma aff_dim_empty_eq [simp]: "aff_dim ({}::'a::euclidean_space set) = -1"
by (simp add: aff_dim_empty [symmetric])
lemma aff_dim_affine_hull [simp]: "aff_dim (affine hull S) = aff_dim S"
unfolding aff_dim_def using hull_hull[of _ S] by auto
lemma aff_dim_affine_hull2:
assumes "affine hull S = affine hull T"
shows "aff_dim S = aff_dim T"
unfolding aff_dim_def using assms by auto
lemma aff_dim_unique:
fixes B V :: "'n::euclidean_space set"
assumes "affine hull B = affine hull V \<and> \<not> affine_dependent B"
shows "of_nat (card B) = aff_dim V + 1"
proof (cases "B = {}")
case True
then have "V = {}"
using assms
by auto
then have "aff_dim V = (-1::int)"
using aff_dim_empty by auto
then show ?thesis
using \<open>B = {}\<close> by auto
next
case False
then obtain a where a: "a \<in> B" by auto
define Lb where "Lb = span ((\<lambda>x. -a+x) ` (B-{a}))"
have "affine_parallel (affine hull B) Lb"
using Lb_def affine_hull_span2[of a B] a
affine_parallel_commut[of "Lb" "(affine hull B)"]
unfolding affine_parallel_def by auto
moreover have "subspace Lb"
using Lb_def subspace_span by auto
ultimately have "aff_dim B = int(dim Lb)"
using aff_dim_parallel_subspace[of B Lb] \<open>B \<noteq> {}\<close> by auto
moreover have "(card B) - 1 = dim Lb" "finite B"
using Lb_def aff_dim_parallel_subspace_aux a assms by auto
ultimately have "of_nat (card B) = aff_dim B + 1"
using \<open>B \<noteq> {}\<close> card_gt_0_iff[of B] by auto
then show ?thesis
using aff_dim_affine_hull2 assms by auto
qed
lemma aff_dim_affine_independent:
fixes B :: "'n::euclidean_space set"
assumes "\<not> affine_dependent B"
shows "of_nat (card B) = aff_dim B + 1"
using aff_dim_unique[of B B] assms by auto
lemma affine_independent_iff_card:
fixes s :: "'a::euclidean_space set"
shows "\<not> affine_dependent s \<longleftrightarrow> finite s \<and> aff_dim s = int(card s) - 1"
apply (rule iffI)
apply (simp add: aff_dim_affine_independent aff_independent_finite)
by (metis affine_basis_exists [of s] aff_dim_unique card_subset_eq diff_add_cancel of_nat_eq_iff)
lemma aff_dim_sing [simp]:
fixes a :: "'n::euclidean_space"
shows "aff_dim {a} = 0"
using aff_dim_affine_independent[of "{a}"] affine_independent_1 by auto
lemma aff_dim_2 [simp]: "aff_dim {a,b} = (if a = b then 0 else 1)"
proof (clarsimp)
assume "a \<noteq> b"
then have "aff_dim{a,b} = card{a,b} - 1"
using affine_independent_2 [of a b] aff_dim_affine_independent by fastforce
also have "\<dots> = 1"
using \<open>a \<noteq> b\<close> by simp
finally show "aff_dim {a, b} = 1" .
qed
lemma aff_dim_inner_basis_exists:
fixes V :: "('n::euclidean_space) set"
shows "\<exists>B. B \<subseteq> V \<and> affine hull B = affine hull V \<and>
\<not> affine_dependent B \<and> of_nat (card B) = aff_dim V + 1"
proof -
obtain B where B: "\<not> affine_dependent B" "B \<subseteq> V" "affine hull B = affine hull V"
using affine_basis_exists[of V] by auto
then have "of_nat(card B) = aff_dim V+1" using aff_dim_unique by auto
with B show ?thesis by auto
qed
lemma aff_dim_le_card:
fixes V :: "'n::euclidean_space set"
assumes "finite V"
shows "aff_dim V \<le> of_nat (card V) - 1"
proof -
obtain B where B: "B \<subseteq> V" "of_nat (card B) = aff_dim V + 1"
using aff_dim_inner_basis_exists[of V] by auto
then have "card B \<le> card V"
using assms card_mono by auto
with B show ?thesis by auto
qed
lemma aff_dim_parallel_eq:
fixes S T :: "'n::euclidean_space set"
assumes "affine_parallel (affine hull S) (affine hull T)"
shows "aff_dim S = aff_dim T"
proof -
{
assume "T \<noteq> {}" "S \<noteq> {}"
then obtain L where L: "subspace L \<and> affine_parallel (affine hull T) L"
using affine_parallel_subspace[of "affine hull T"]
affine_affine_hull[of T]
by auto
then have "aff_dim T = int (dim L)"
using aff_dim_parallel_subspace \<open>T \<noteq> {}\<close> by auto
moreover have *: "subspace L \<and> affine_parallel (affine hull S) L"
using L affine_parallel_assoc[of "affine hull S" "affine hull T" L] assms by auto
moreover from * have "aff_dim S = int (dim L)"
using aff_dim_parallel_subspace \<open>S \<noteq> {}\<close> by auto
ultimately have ?thesis by auto
}
moreover
{
assume "S = {}"
then have "S = {}" and "T = {}"
using assms
unfolding affine_parallel_def
by auto
then have ?thesis using aff_dim_empty by auto
}
moreover
{
assume "T = {}"
then have "S = {}" and "T = {}"
using assms
unfolding affine_parallel_def
by auto
then have ?thesis
using aff_dim_empty by auto
}
ultimately show ?thesis by blast
qed
lemma aff_dim_translation_eq:
"aff_dim ((+) a ` S) = aff_dim S" for a :: "'n::euclidean_space"
proof -
have "affine_parallel (affine hull S) (affine hull ((\<lambda>x. a + x) ` S))"
unfolding affine_parallel_def
apply (rule exI[of _ "a"])
using affine_hull_translation[of a S]
apply auto
done
then show ?thesis
using aff_dim_parallel_eq[of S "(\<lambda>x. a + x) ` S"] by auto
qed
lemma aff_dim_translation_eq_subtract:
"aff_dim ((\<lambda>x. x - a) ` S) = aff_dim S" for a :: "'n::euclidean_space"
using aff_dim_translation_eq [of "- a"] by (simp cong: image_cong_simp)
lemma aff_dim_affine:
fixes S L :: "'n::euclidean_space set"
assumes "S \<noteq> {}"
and "affine S"
and "subspace L"
and "affine_parallel S L"
shows "aff_dim S = int (dim L)"
proof -
have *: "affine hull S = S"
using assms affine_hull_eq[of S] by auto
then have "affine_parallel (affine hull S) L"
using assms by (simp add: *)
then show ?thesis
using assms aff_dim_parallel_subspace[of S L] by blast
qed
lemma dim_affine_hull:
fixes S :: "'n::euclidean_space set"
shows "dim (affine hull S) = dim S"
proof -
have "dim (affine hull S) \<ge> dim S"
using dim_subset by auto
moreover have "dim (span S) \<ge> dim (affine hull S)"
using dim_subset affine_hull_subset_span by blast
moreover have "dim (span S) = dim S"
using dim_span by auto
ultimately show ?thesis by auto
qed
lemma aff_dim_subspace:
fixes S :: "'n::euclidean_space set"
assumes "subspace S"
shows "aff_dim S = int (dim S)"
proof (cases "S={}")
case True with assms show ?thesis
by (simp add: subspace_affine)
next
case False
with aff_dim_affine[of S S] assms subspace_imp_affine[of S] affine_parallel_reflex[of S] subspace_affine
show ?thesis by auto
qed
lemma aff_dim_zero:
fixes S :: "'n::euclidean_space set"
assumes "0 \<in> affine hull S"
shows "aff_dim S = int (dim S)"
proof -
have "subspace (affine hull S)"
using subspace_affine[of "affine hull S"] affine_affine_hull assms
by auto
then have "aff_dim (affine hull S) = int (dim (affine hull S))"
using assms aff_dim_subspace[of "affine hull S"] by auto
then show ?thesis
using aff_dim_affine_hull[of S] dim_affine_hull[of S]
by auto
qed
lemma aff_dim_eq_dim:
"aff_dim S = int (dim ((+) (- a) ` S))" if "a \<in> affine hull S"
for S :: "'n::euclidean_space set"
proof -
have "0 \<in> affine hull (+) (- a) ` S"
unfolding affine_hull_translation
using that by (simp add: ac_simps)
with aff_dim_zero show ?thesis
by (metis aff_dim_translation_eq)
qed
lemma aff_dim_eq_dim_subtract:
"aff_dim S = int (dim ((\<lambda>x. x - a) ` S))" if "a \<in> affine hull S"
for S :: "'n::euclidean_space set"
using aff_dim_eq_dim [of a] that by (simp cong: image_cong_simp)
lemma aff_dim_UNIV [simp]: "aff_dim (UNIV :: 'n::euclidean_space set) = int(DIM('n))"
using aff_dim_subspace[of "(UNIV :: 'n::euclidean_space set)"]
dim_UNIV[where 'a="'n::euclidean_space"]
by auto
lemma aff_dim_geq:
fixes V :: "'n::euclidean_space set"
shows "aff_dim V \<ge> -1"
proof -
obtain B where "affine hull B = affine hull V"
and "\<not> affine_dependent B"
and "int (card B) = aff_dim V + 1"
using aff_dim_basis_exists by auto
then show ?thesis by auto
qed
lemma aff_dim_negative_iff [simp]:
fixes S :: "'n::euclidean_space set"
shows "aff_dim S < 0 \<longleftrightarrow>S = {}"
by (metis aff_dim_empty aff_dim_geq diff_0 eq_iff zle_diff1_eq)
lemma aff_lowdim_subset_hyperplane:
fixes S :: "'a::euclidean_space set"
assumes "aff_dim S < DIM('a)"
obtains a b where "a \<noteq> 0" "S \<subseteq> {x. a \<bullet> x = b}"
proof (cases "S={}")
case True
moreover
have "(SOME b. b \<in> Basis) \<noteq> 0"
by (metis norm_some_Basis norm_zero zero_neq_one)
ultimately show ?thesis
using that by blast
next
case False
then obtain c S' where "c \<notin> S'" "S = insert c S'"
by (meson equals0I mk_disjoint_insert)
have "dim ((+) (-c) ` S) < DIM('a)"
by (metis \<open>S = insert c S'\<close> aff_dim_eq_dim assms hull_inc insertI1 of_nat_less_imp_less)
then obtain a where "a \<noteq> 0" "span ((+) (-c) ` S) \<subseteq> {x. a \<bullet> x = 0}"
using lowdim_subset_hyperplane by blast
moreover
have "a \<bullet> w = a \<bullet> c" if "span ((+) (- c) ` S) \<subseteq> {x. a \<bullet> x = 0}" "w \<in> S" for w
proof -
have "w-c \<in> span ((+) (- c) ` S)"
by (simp add: span_base \<open>w \<in> S\<close>)
with that have "w-c \<in> {x. a \<bullet> x = 0}"
by blast
then show ?thesis
by (auto simp: algebra_simps)
qed
ultimately have "S \<subseteq> {x. a \<bullet> x = a \<bullet> c}"
by blast
then show ?thesis
by (rule that[OF \<open>a \<noteq> 0\<close>])
qed
lemma affine_independent_card_dim_diffs:
fixes S :: "'a :: euclidean_space set"
assumes "\<not> affine_dependent S" "a \<in> S"
shows "card S = dim {x - a|x. x \<in> S} + 1"
proof -
have 1: "{b - a|b. b \<in> (S - {a})} \<subseteq> {x - a|x. x \<in> S}" by auto
have 2: "x - a \<in> span {b - a |b. b \<in> S - {a}}" if "x \<in> S" for x
proof (cases "x = a")
case True then show ?thesis by (simp add: span_clauses)
next
case False then show ?thesis
using assms by (blast intro: span_base that)
qed
have "\<not> affine_dependent (insert a S)"
by (simp add: assms insert_absorb)
then have 3: "independent {b - a |b. b \<in> S - {a}}"
using dependent_imp_affine_dependent by fastforce
have "{b - a |b. b \<in> S - {a}} = (\<lambda>b. b-a) ` (S - {a})"
by blast
then have "card {b - a |b. b \<in> S - {a}} = card ((\<lambda>b. b-a) ` (S - {a}))"
by simp
also have "\<dots> = card (S - {a})"
by (metis (no_types, lifting) card_image diff_add_cancel inj_onI)
also have "\<dots> = card S - 1"
by (simp add: aff_independent_finite assms)
finally have 4: "card {b - a |b. b \<in> S - {a}} = card S - 1" .
have "finite S"
by (meson assms aff_independent_finite)
with \<open>a \<in> S\<close> have "card S \<noteq> 0" by auto
moreover have "dim {x - a |x. x \<in> S} = card S - 1"
using 2 by (blast intro: dim_unique [OF 1 _ 3 4])
ultimately show ?thesis
by auto
qed
lemma independent_card_le_aff_dim:
fixes B :: "'n::euclidean_space set"
assumes "B \<subseteq> V"
assumes "\<not> affine_dependent B"
shows "int (card B) \<le> aff_dim V + 1"
proof -
obtain T where T: "\<not> affine_dependent T \<and> B \<subseteq> T \<and> T \<subseteq> V \<and> affine hull T = affine hull V"
by (metis assms extend_to_affine_basis[of B V])
then have "of_nat (card T) = aff_dim V + 1"
using aff_dim_unique by auto
then show ?thesis
using T card_mono[of T B] aff_independent_finite[of T] by auto
qed
lemma aff_dim_subset:
fixes S T :: "'n::euclidean_space set"
assumes "S \<subseteq> T"
shows "aff_dim S \<le> aff_dim T"
proof -
obtain B where B: "\<not> affine_dependent B" "B \<subseteq> S" "affine hull B = affine hull S"
"of_nat (card B) = aff_dim S + 1"
using aff_dim_inner_basis_exists[of S] by auto
then have "int (card B) \<le> aff_dim T + 1"
using assms independent_card_le_aff_dim[of B T] by auto
with B show ?thesis by auto
qed
lemma aff_dim_le_DIM:
fixes S :: "'n::euclidean_space set"
shows "aff_dim S \<le> int (DIM('n))"
proof -
have "aff_dim (UNIV :: 'n::euclidean_space set) = int(DIM('n))"
using aff_dim_UNIV by auto
then show "aff_dim (S:: 'n::euclidean_space set) \<le> int(DIM('n))"
using aff_dim_subset[of S "(UNIV :: ('n::euclidean_space) set)"] subset_UNIV by auto
qed
lemma affine_dim_equal:
fixes S :: "'n::euclidean_space set"
assumes "affine S" "affine T" "S \<noteq> {}" "S \<subseteq> T" "aff_dim S = aff_dim T"
shows "S = T"
proof -
obtain a where "a \<in> S" using assms by auto
then have "a \<in> T" using assms by auto
define LS where "LS = {y. \<exists>x \<in> S. (-a) + x = y}"
then have ls: "subspace LS" "affine_parallel S LS"
using assms parallel_subspace_explicit[of S a LS] \<open>a \<in> S\<close> by auto
then have h1: "int(dim LS) = aff_dim S"
using assms aff_dim_affine[of S LS] by auto
have "T \<noteq> {}" using assms by auto
define LT where "LT = {y. \<exists>x \<in> T. (-a) + x = y}"
then have lt: "subspace LT \<and> affine_parallel T LT"
using assms parallel_subspace_explicit[of T a LT] \<open>a \<in> T\<close> by auto
then have "int(dim LT) = aff_dim T"
using assms aff_dim_affine[of T LT] \<open>T \<noteq> {}\<close> by auto
then have "dim LS = dim LT"
using h1 assms by auto
moreover have "LS \<le> LT"
using LS_def LT_def assms by auto
ultimately have "LS = LT"
using subspace_dim_equal[of LS LT] ls lt by auto
moreover have "S = {x. \<exists>y \<in> LS. a+y=x}"
using LS_def by auto
moreover have "T = {x. \<exists>y \<in> LT. a+y=x}"
using LT_def by auto
ultimately show ?thesis by auto
qed
lemma aff_dim_eq_0:
fixes S :: "'a::euclidean_space set"
shows "aff_dim S = 0 \<longleftrightarrow> (\<exists>a. S = {a})"
proof (cases "S = {}")
case True
then show ?thesis
by auto
next
case False
then obtain a where "a \<in> S" by auto
show ?thesis
proof safe
assume 0: "aff_dim S = 0"
have "\<not> {a,b} \<subseteq> S" if "b \<noteq> a" for b
by (metis "0" aff_dim_2 aff_dim_subset not_one_le_zero that)
then show "\<exists>a. S = {a}"
using \<open>a \<in> S\<close> by blast
qed auto
qed
lemma affine_hull_UNIV:
fixes S :: "'n::euclidean_space set"
assumes "aff_dim S = int(DIM('n))"
shows "affine hull S = (UNIV :: ('n::euclidean_space) set)"
proof -
have "S \<noteq> {}"
using assms aff_dim_empty[of S] by auto
have h0: "S \<subseteq> affine hull S"
using hull_subset[of S _] by auto
have h1: "aff_dim (UNIV :: ('n::euclidean_space) set) = aff_dim S"
using aff_dim_UNIV assms by auto
then have h2: "aff_dim (affine hull S) \<le> aff_dim (UNIV :: ('n::euclidean_space) set)"
using aff_dim_le_DIM[of "affine hull S"] assms h0 by auto
have h3: "aff_dim S \<le> aff_dim (affine hull S)"
using h0 aff_dim_subset[of S "affine hull S"] assms by auto
then have h4: "aff_dim (affine hull S) = aff_dim (UNIV :: ('n::euclidean_space) set)"
using h0 h1 h2 by auto
then show ?thesis
using affine_dim_equal[of "affine hull S" "(UNIV :: ('n::euclidean_space) set)"]
affine_affine_hull[of S] affine_UNIV assms h4 h0 \<open>S \<noteq> {}\<close>
by auto
qed
lemma disjoint_affine_hull:
fixes s :: "'n::euclidean_space set"
assumes "\<not> affine_dependent s" "t \<subseteq> s" "u \<subseteq> s" "t \<inter> u = {}"
shows "(affine hull t) \<inter> (affine hull u) = {}"
proof -
have "finite s" using assms by (simp add: aff_independent_finite)
then have "finite t" "finite u" using assms finite_subset by blast+
{ fix y
assume yt: "y \<in> affine hull t" and yu: "y \<in> affine hull u"
then obtain a b
where a1 [simp]: "sum a t = 1" and [simp]: "sum (\<lambda>v. a v *\<^sub>R v) t = y"
and [simp]: "sum b u = 1" "sum (\<lambda>v. b v *\<^sub>R v) u = y"
by (auto simp: affine_hull_finite \<open>finite t\<close> \<open>finite u\<close>)
define c where "c x = (if x \<in> t then a x else if x \<in> u then -(b x) else 0)" for x
have [simp]: "s \<inter> t = t" "s \<inter> - t \<inter> u = u" using assms by auto
have "sum c s = 0"
by (simp add: c_def comm_monoid_add_class.sum.If_cases \<open>finite s\<close> sum_negf)
moreover have "\<not> (\<forall>v\<in>s. c v = 0)"
by (metis (no_types) IntD1 \<open>s \<inter> t = t\<close> a1 c_def sum.neutral zero_neq_one)
moreover have "(\<Sum>v\<in>s. c v *\<^sub>R v) = 0"
by (simp add: c_def if_smult sum_negf
comm_monoid_add_class.sum.If_cases \<open>finite s\<close>)
ultimately have False
using assms \<open>finite s\<close> by (auto simp: affine_dependent_explicit)
}
then show ?thesis by blast
qed
end