src/HOL/Groups_Big.thy

modernized theory setup;

(*  Title:      HOL/Groups_Big.thy
    Author:     Tobias Nipkow, Lawrence C Paulson and Markus Wenzel
                with contributions by Jeremy Avigad
*)

header {* Big sum and product over finite (non-empty) sets *}

theory Groups_Big
imports Finite_Set
begin

subsection {* Generic monoid operation over a set *}

no_notation times (infixl "*" 70)
no_notation Groups.one ("1")

locale comm_monoid_set = comm_monoid
begin

interpretation comp_fun_commute f
  by default (simp add: fun_eq_iff left_commute)

interpretation comp?: comp_fun_commute "f \<circ> g"
  by (fact comp_comp_fun_commute)

definition F :: "('b \<Rightarrow> 'a) \<Rightarrow> 'b set \<Rightarrow> 'a"
where
  eq_fold: "F g A = Finite_Set.fold (f \<circ> g) 1 A"

lemma infinite [simp]:
  "\<not> finite A \<Longrightarrow> F g A = 1"
  by (simp add: eq_fold)

lemma empty [simp]:
  "F g {} = 1"
  by (simp add: eq_fold)

lemma insert [simp]:
  assumes "finite A" and "x \<notin> A"
  shows "F g (insert x A) = g x * F g A"
  using assms by (simp add: eq_fold)

lemma remove:
  assumes "finite A" and "x \<in> A"
  shows "F g A = g x * F g (A - {x})"
proof -
  from `x \<in> A` obtain B where A: "A = insert x B" and "x \<notin> B"
    by (auto dest: mk_disjoint_insert)
  moreover from `finite A` A have "finite B" by simp
  ultimately show ?thesis by simp
qed

lemma insert_remove:
  assumes "finite A"
  shows "F g (insert x A) = g x * F g (A - {x})"
  using assms by (cases "x \<in> A") (simp_all add: remove insert_absorb)

lemma neutral:
  assumes "\<forall>x\<in>A. g x = 1"
  shows "F g A = 1"
  using assms by (induct A rule: infinite_finite_induct) simp_all

lemma neutral_const [simp]:
  "F (\<lambda>_. 1) A = 1"
  by (simp add: neutral)

lemma union_inter:
  assumes "finite A" and "finite B"
  shows "F g (A \<union> B) * F g (A \<inter> B) = F g A * F g B"
  -- {* The reversed orientation looks more natural, but LOOPS as a simprule! *}
using assms proof (induct A)
  case empty then show ?case by simp
next
  case (insert x A) then show ?case
    by (auto simp add: insert_absorb Int_insert_left commute [of _ "g x"] assoc left_commute)
qed

corollary union_inter_neutral:
  assumes "finite A" and "finite B"
  and I0: "\<forall>x \<in> A \<inter> B. g x = 1"
  shows "F g (A \<union> B) = F g A * F g B"
  using assms by (simp add: union_inter [symmetric] neutral)

corollary union_disjoint:
  assumes "finite A" and "finite B"
  assumes "A \<inter> B = {}"
  shows "F g (A \<union> B) = F g A * F g B"
  using assms by (simp add: union_inter_neutral)

lemma subset_diff:
  assumes "B \<subseteq> A" and "finite A"
  shows "F g A = F g (A - B) * F g B"
proof -
  from assms have "finite (A - B)" by auto
  moreover from assms have "finite B" by (rule finite_subset)
  moreover from assms have "(A - B) \<inter> B = {}" by auto
  ultimately have "F g (A - B \<union> B) = F g (A - B) * F g B" by (rule union_disjoint)
  moreover from assms have "A \<union> B = A" by auto
  ultimately show ?thesis by simp
qed

lemma setdiff_irrelevant:
  assumes "finite A"
  shows "F g (A - {x. g x = z}) = F g A"
  using assms by (induct A) (simp_all add: insert_Diff_if) 
  
lemma not_neutral_contains_not_neutral:
  assumes "F g A \<noteq> z"
  obtains a where "a \<in> A" and "g a \<noteq> z"
proof -
  from assms have "\<exists>a\<in>A. g a \<noteq> z"
  proof (induct A rule: infinite_finite_induct)
    case (insert a A)
    then show ?case by simp (rule, simp)
  qed simp_all
  with that show thesis by blast
qed

lemma reindex:
  assumes "inj_on h A"
  shows "F g (h ` A) = F (g \<circ> h) A"
proof (cases "finite A")
  case True
  with assms show ?thesis by (simp add: eq_fold fold_image comp_assoc)
next
  case False with assms have "\<not> finite (h ` A)" by (blast dest: finite_imageD)
  with False show ?thesis by simp
qed

lemma cong:
  assumes "A = B"
  assumes g_h: "\<And>x. x \<in> B \<Longrightarrow> g x = h x"
  shows "F g A = F h B"
proof (cases "finite A")
  case True
  then have "\<And>C. C \<subseteq> A \<longrightarrow> (\<forall>x\<in>C. g x = h x) \<longrightarrow> F g C = F h C"
  proof induct
    case empty then show ?case by simp
  next
    case (insert x F) then show ?case apply -
    apply (simp add: subset_insert_iff, clarify)
    apply (subgoal_tac "finite C")
      prefer 2 apply (blast dest: finite_subset [rotated])
    apply (subgoal_tac "C = insert x (C - {x})")
      prefer 2 apply blast
    apply (erule ssubst)
    apply (simp add: Ball_def del: insert_Diff_single)
    done
  qed
  with `A = B` g_h show ?thesis by simp
next
  case False
  with `A = B` show ?thesis by simp
qed

lemma strong_cong [cong]:
  assumes "A = B" "\<And>x. x \<in> B =simp=> g x = h x"
  shows "F (\<lambda>x. g x) A = F (\<lambda>x. h x) B"
  by (rule cong) (insert assms, simp_all add: simp_implies_def)

lemma UNION_disjoint:
  assumes "finite I" and "\<forall>i\<in>I. finite (A i)"
  and "\<forall>i\<in>I. \<forall>j\<in>I. i \<noteq> j \<longrightarrow> A i \<inter> A j = {}"
  shows "F g (UNION I A) = F (\<lambda>x. F g (A x)) I"
apply (insert assms)
apply (induct rule: finite_induct)
apply simp
apply atomize
apply (subgoal_tac "\<forall>i\<in>Fa. x \<noteq> i")
 prefer 2 apply blast
apply (subgoal_tac "A x Int UNION Fa A = {}")
 prefer 2 apply blast
apply (simp add: union_disjoint)
done

lemma Union_disjoint:
  assumes "\<forall>A\<in>C. finite A" "\<forall>A\<in>C. \<forall>B\<in>C. A \<noteq> B \<longrightarrow> A \<inter> B = {}"
  shows "F g (Union C) = F (F g) C"
proof cases
  assume "finite C"
  from UNION_disjoint [OF this assms]
  show ?thesis by simp
qed (auto dest: finite_UnionD intro: infinite)

lemma distrib:
  "F (\<lambda>x. g x * h x) A = F g A * F h A"
  using assms by (induct A rule: infinite_finite_induct) (simp_all add: assoc commute left_commute)

lemma Sigma:
  "finite A \<Longrightarrow> \<forall>x\<in>A. finite (B x) \<Longrightarrow> F (\<lambda>x. F (g x) (B x)) A = F (split g) (SIGMA x:A. B x)"
apply (subst Sigma_def)
apply (subst UNION_disjoint, assumption, simp)
 apply blast
apply (rule cong)
apply rule
apply (simp add: fun_eq_iff)
apply (subst UNION_disjoint, simp, simp)
 apply blast
apply (simp add: comp_def)
done

lemma related: 
  assumes Re: "R 1 1" 
  and Rop: "\<forall>x1 y1 x2 y2. R x1 x2 \<and> R y1 y2 \<longrightarrow> R (x1 * y1) (x2 * y2)" 
  and fS: "finite S" and Rfg: "\<forall>x\<in>S. R (h x) (g x)"
  shows "R (F h S) (F g S)"
  using fS by (rule finite_subset_induct) (insert assms, auto)

lemma eq_general:
  assumes h: "\<forall>y\<in>S'. \<exists>!x. x \<in> S \<and> h x = y" 
  and f12:  "\<forall>x\<in>S. h x \<in> S' \<and> f2 (h x) = f1 x"
  shows "F f1 S = F f2 S'"
proof-
  from h f12 have hS: "h ` S = S'" by blast
  {fix x y assume H: "x \<in> S" "y \<in> S" "h x = h y"
    from f12 h H  have "x = y" by auto }
  hence hinj: "inj_on h S" unfolding inj_on_def Ex1_def by blast
  from f12 have th: "\<And>x. x \<in> S \<Longrightarrow> (f2 \<circ> h) x = f1 x" by auto 
  from hS have "F f2 S' = F f2 (h ` S)" by simp
  also have "\<dots> = F (f2 o h) S" using reindex [OF hinj, of f2] .
  also have "\<dots> = F f1 S " using th cong [of _ _ "f2 o h" f1]
    by blast
  finally show ?thesis ..
qed

lemma eq_general_reverses:
  assumes kh: "\<And>y. y \<in> T \<Longrightarrow> k y \<in> S \<and> h (k y) = y"
  and hk: "\<And>x. x \<in> S \<Longrightarrow> h x \<in> T \<and> k (h x) = x \<and> g (h x) = j x"
  shows "F j S = F g T"
  (* metis solves it, but not yet available here *)
  apply (rule eq_general [of T S h g j])
  apply (rule ballI)
  apply (frule kh)
  apply (rule ex1I[])
  apply blast
  apply clarsimp
  apply (drule hk) apply simp
  apply (rule sym)
  apply (erule conjunct1[OF conjunct2[OF hk]])
  apply (rule ballI)
  apply (drule hk)
  apply blast
  done

lemma mono_neutral_cong_left:
  assumes "finite T" and "S \<subseteq> T" and "\<forall>i \<in> T - S. h i = 1"
  and "\<And>x. x \<in> S \<Longrightarrow> g x = h x" shows "F g S = F h T"
proof-
  have eq: "T = S \<union> (T - S)" using `S \<subseteq> T` by blast
  have d: "S \<inter> (T - S) = {}" using `S \<subseteq> T` by blast
  from `finite T` `S \<subseteq> T` have f: "finite S" "finite (T - S)"
    by (auto intro: finite_subset)
  show ?thesis using assms(4)
    by (simp add: union_disjoint [OF f d, unfolded eq [symmetric]] neutral [OF assms(3)])
qed

lemma mono_neutral_cong_right:
  "\<lbrakk> finite T; S \<subseteq> T; \<forall>i \<in> T - S. g i = 1; \<And>x. x \<in> S \<Longrightarrow> g x = h x \<rbrakk>
   \<Longrightarrow> F g T = F h S"
  by (auto intro!: mono_neutral_cong_left [symmetric])

lemma mono_neutral_left:
  "\<lbrakk> finite T; S \<subseteq> T; \<forall>i \<in> T - S. g i = 1 \<rbrakk> \<Longrightarrow> F g S = F g T"
  by (blast intro: mono_neutral_cong_left)

lemma mono_neutral_right:
  "\<lbrakk> finite T;  S \<subseteq> T;  \<forall>i \<in> T - S. g i = 1 \<rbrakk> \<Longrightarrow> F g T = F g S"
  by (blast intro!: mono_neutral_left [symmetric])

lemma delta: 
  assumes fS: "finite S"
  shows "F (\<lambda>k. if k = a then b k else 1) S = (if a \<in> S then b a else 1)"
proof-
  let ?f = "(\<lambda>k. if k=a then b k else 1)"
  { assume a: "a \<notin> S"
    hence "\<forall>k\<in>S. ?f k = 1" by simp
    hence ?thesis  using a by simp }
  moreover
  { assume a: "a \<in> S"
    let ?A = "S - {a}"
    let ?B = "{a}"
    have eq: "S = ?A \<union> ?B" using a by blast 
    have dj: "?A \<inter> ?B = {}" by simp
    from fS have fAB: "finite ?A" "finite ?B" by auto  
    have "F ?f S = F ?f ?A * F ?f ?B"
      using union_disjoint [OF fAB dj, of ?f, unfolded eq [symmetric]]
      by simp
    then have ?thesis using a by simp }
  ultimately show ?thesis by blast
qed

lemma delta': 
  assumes fS: "finite S"
  shows "F (\<lambda>k. if a = k then b k else 1) S = (if a \<in> S then b a else 1)"
  using delta [OF fS, of a b, symmetric] by (auto intro: cong)

lemma If_cases:
  fixes P :: "'b \<Rightarrow> bool" and g h :: "'b \<Rightarrow> 'a"
  assumes fA: "finite A"
  shows "F (\<lambda>x. if P x then h x else g x) A =
    F h (A \<inter> {x. P x}) * F g (A \<inter> - {x. P x})"
proof -
  have a: "A = A \<inter> {x. P x} \<union> A \<inter> -{x. P x}" 
          "(A \<inter> {x. P x}) \<inter> (A \<inter> -{x. P x}) = {}" 
    by blast+
  from fA 
  have f: "finite (A \<inter> {x. P x})" "finite (A \<inter> -{x. P x})" by auto
  let ?g = "\<lambda>x. if P x then h x else g x"
  from union_disjoint [OF f a(2), of ?g] a(1)
  show ?thesis
    by (subst (1 2) cong) simp_all
qed

lemma cartesian_product:
   "F (\<lambda>x. F (g x) B) A = F (split g) (A <*> B)"
apply (rule sym)
apply (cases "finite A") 
 apply (cases "finite B") 
  apply (simp add: Sigma)
 apply (cases "A={}", simp)
 apply simp
apply (auto intro: infinite dest: finite_cartesian_productD2)
apply (cases "B = {}") apply (auto intro: infinite dest: finite_cartesian_productD1)
done

end

notation times (infixl "*" 70)
notation Groups.one ("1")


subsection {* Generalized summation over a set *}

context comm_monoid_add
begin

definition setsum :: "('b \<Rightarrow> 'a) \<Rightarrow> 'b set \<Rightarrow> 'a"
where
  "setsum = comm_monoid_set.F plus 0"

sublocale setsum!: comm_monoid_set plus 0
where
  "comm_monoid_set.F plus 0 = setsum"
proof -
  show "comm_monoid_set plus 0" ..
  then interpret setsum!: comm_monoid_set plus 0 .
  from setsum_def show "comm_monoid_set.F plus 0 = setsum" by rule
qed

abbreviation
  Setsum ("\<Sum>_" [1000] 999) where
  "\<Sum>A \<equiv> setsum (%x. x) A"

end

text{* Now: lot's of fancy syntax. First, @{term "setsum (%x. e) A"} is
written @{text"\<Sum>x\<in>A. e"}. *}

syntax
  "_setsum" :: "pttrn => 'a set => 'b => 'b::comm_monoid_add"    ("(3SUM _:_. _)" [0, 51, 10] 10)
syntax (xsymbols)
  "_setsum" :: "pttrn => 'a set => 'b => 'b::comm_monoid_add"    ("(3\<Sum>_\<in>_. _)" [0, 51, 10] 10)
syntax (HTML output)
  "_setsum" :: "pttrn => 'a set => 'b => 'b::comm_monoid_add"    ("(3\<Sum>_\<in>_. _)" [0, 51, 10] 10)

translations -- {* Beware of argument permutation! *}
  "SUM i:A. b" == "CONST setsum (%i. b) A"
  "\<Sum>i\<in>A. b" == "CONST setsum (%i. b) A"

text{* Instead of @{term"\<Sum>x\<in>{x. P}. e"} we introduce the shorter
 @{text"\<Sum>x|P. e"}. *}

syntax
  "_qsetsum" :: "pttrn \<Rightarrow> bool \<Rightarrow> 'a \<Rightarrow> 'a" ("(3SUM _ |/ _./ _)" [0,0,10] 10)
syntax (xsymbols)
  "_qsetsum" :: "pttrn \<Rightarrow> bool \<Rightarrow> 'a \<Rightarrow> 'a" ("(3\<Sum>_ | (_)./ _)" [0,0,10] 10)
syntax (HTML output)
  "_qsetsum" :: "pttrn \<Rightarrow> bool \<Rightarrow> 'a \<Rightarrow> 'a" ("(3\<Sum>_ | (_)./ _)" [0,0,10] 10)

translations
  "SUM x|P. t" => "CONST setsum (%x. t) {x. P}"
  "\<Sum>x|P. t" => "CONST setsum (%x. t) {x. P}"

print_translation {*
let
  fun setsum_tr' [Abs (x, Tx, t), Const (@{const_syntax Collect}, _) $ Abs (y, Ty, P)] =
        if x <> y then raise Match
        else
          let
            val x' = Syntax_Trans.mark_bound_body (x, Tx);
            val t' = subst_bound (x', t);
            val P' = subst_bound (x', P);
          in
            Syntax.const @{syntax_const "_qsetsum"} $ Syntax_Trans.mark_bound_abs (x, Tx) $ P' $ t'
          end
    | setsum_tr' _ = raise Match;
in [(@{const_syntax setsum}, K setsum_tr')] end
*}

text {* TODO These are candidates for generalization *}

context comm_monoid_add
begin

lemma setsum_reindex_id: 
  "inj_on f B ==> setsum f B = setsum id (f ` B)"
  by (simp add: setsum.reindex)

lemma setsum_reindex_nonzero:
  assumes fS: "finite S"
  and nz: "\<And>x y. x \<in> S \<Longrightarrow> y \<in> S \<Longrightarrow> x \<noteq> y \<Longrightarrow> f x = f y \<Longrightarrow> h (f x) = 0"
  shows "setsum h (f ` S) = setsum (h \<circ> f) S"
using nz proof (induct rule: finite_induct [OF fS])
  case 1 thus ?case by simp
next
  case (2 x F) 
  { assume fxF: "f x \<in> f ` F" hence "\<exists>y \<in> F . f y = f x" by auto
    then obtain y where y: "y \<in> F" "f x = f y" by auto 
    from "2.hyps" y have xy: "x \<noteq> y" by auto
    from "2.prems" [of x y] "2.hyps" xy y have h0: "h (f x) = 0" by simp
    have "setsum h (f ` insert x F) = setsum h (f ` F)" using fxF by auto
    also have "\<dots> = setsum (h o f) (insert x F)" 
      unfolding setsum.insert[OF `finite F` `x\<notin>F`]
      using h0
      apply (simp cong del: setsum.strong_cong)
      apply (rule "2.hyps"(3))
      apply (rule_tac y="y" in  "2.prems")
      apply simp_all
      done
    finally have ?case . }
  moreover
  { assume fxF: "f x \<notin> f ` F"
    have "setsum h (f ` insert x F) = h (f x) + setsum h (f ` F)" 
      using fxF "2.hyps" by simp 
    also have "\<dots> = setsum (h o f) (insert x F)"
      unfolding setsum.insert[OF `finite F` `x\<notin>F`]
      apply (simp cong del: setsum.strong_cong)
      apply (rule cong [OF refl [of "op + (h (f x))"]])
      apply (rule "2.hyps"(3))
      apply (rule_tac y="y" in  "2.prems")
      apply simp_all
      done
    finally have ?case . }
  ultimately show ?case by blast
qed

lemma setsum_cong2:
  "(\<And>x. x \<in> A \<Longrightarrow> f x = g x) \<Longrightarrow> setsum f A = setsum g A"
  by (auto intro: setsum.cong)

lemma setsum_reindex_cong:
   "[|inj_on f A; B = f ` A; !!a. a:A \<Longrightarrow> g a = h (f a)|] 
    ==> setsum h B = setsum g A"
  by (simp add: setsum.reindex)

lemma setsum_restrict_set:
  assumes fA: "finite A"
  shows "setsum f (A \<inter> B) = setsum (\<lambda>x. if x \<in> B then f x else 0) A"
proof-
  from fA have fab: "finite (A \<inter> B)" by auto
  have aba: "A \<inter> B \<subseteq> A" by blast
  let ?g = "\<lambda>x. if x \<in> A\<inter>B then f x else 0"
  from setsum.mono_neutral_left [OF fA aba, of ?g]
  show ?thesis by simp
qed

lemma setsum_Union_disjoint:
  assumes "\<forall>A\<in>C. finite A" "\<forall>A\<in>C. \<forall>B\<in>C. A \<noteq> B \<longrightarrow> A Int B = {}"
  shows "setsum f (Union C) = setsum (setsum f) C"
  using assms by (fact setsum.Union_disjoint)

lemma setsum_cartesian_product:
  "(\<Sum>x\<in>A. (\<Sum>y\<in>B. f x y)) = (\<Sum>(x,y) \<in> A <*> B. f x y)"
  by (fact setsum.cartesian_product)

lemma setsum_UNION_zero:
  assumes fS: "finite S" and fSS: "\<forall>T \<in> S. finite T"
  and f0: "\<And>T1 T2 x. T1\<in>S \<Longrightarrow> T2\<in>S \<Longrightarrow> T1 \<noteq> T2 \<Longrightarrow> x \<in> T1 \<Longrightarrow> x \<in> T2 \<Longrightarrow> f x = 0"
  shows "setsum f (\<Union>S) = setsum (\<lambda>T. setsum f T) S"
  using fSS f0
proof(induct rule: finite_induct[OF fS])
  case 1 thus ?case by simp
next
  case (2 T F)
  then have fTF: "finite T" "\<forall>T\<in>F. finite T" "finite F" and TF: "T \<notin> F" 
    and H: "setsum f (\<Union> F) = setsum (setsum f) F" by auto
  from fTF have fUF: "finite (\<Union>F)" by auto
  from "2.prems" TF fTF
  show ?case 
    by (auto simp add: H [symmetric] intro: setsum.union_inter_neutral [OF fTF(1) fUF, of f])
qed

text {* Commuting outer and inner summation *}

lemma setsum_commute:
  "(\<Sum>i\<in>A. \<Sum>j\<in>B. f i j) = (\<Sum>j\<in>B. \<Sum>i\<in>A. f i j)"
proof (simp add: setsum_cartesian_product)
  have "(\<Sum>(x,y) \<in> A <*> B. f x y) =
    (\<Sum>(y,x) \<in> (%(i, j). (j, i)) ` (A \<times> B). f x y)"
    (is "?s = _")
    apply (simp add: setsum.reindex [where h = "%(i, j). (j, i)"] swap_inj_on)
    apply (simp add: split_def)
    done
  also have "... = (\<Sum>(y,x)\<in>B \<times> A. f x y)"
    (is "_ = ?t")
    apply (simp add: swap_product)
    done
  finally show "?s = ?t" .
qed

lemma setsum_Plus:
  fixes A :: "'a set" and B :: "'b set"
  assumes fin: "finite A" "finite B"
  shows "setsum f (A <+> B) = setsum (f \<circ> Inl) A + setsum (f \<circ> Inr) B"
proof -
  have "A <+> B = Inl ` A \<union> Inr ` B" by auto
  moreover from fin have "finite (Inl ` A :: ('a + 'b) set)" "finite (Inr ` B :: ('a + 'b) set)"
    by auto
  moreover have "Inl ` A \<inter> Inr ` B = ({} :: ('a + 'b) set)" by auto
  moreover have "inj_on (Inl :: 'a \<Rightarrow> 'a + 'b) A" "inj_on (Inr :: 'b \<Rightarrow> 'a + 'b) B" by(auto intro: inj_onI)
  ultimately show ?thesis using fin by(simp add: setsum.union_disjoint setsum.reindex)
qed

end

text {* TODO These are legacy *}

lemma setsum_empty:
  "setsum f {} = 0"
  by (fact setsum.empty)

lemma setsum_insert:
  "finite F ==> a \<notin> F ==> setsum f (insert a F) = f a + setsum f F"
  by (fact setsum.insert)

lemma setsum_infinite:
  "~ finite A ==> setsum f A = 0"
  by (fact setsum.infinite)

lemma setsum_reindex:
  "inj_on f B \<Longrightarrow> setsum h (f ` B) = setsum (h \<circ> f) B"
  by (fact setsum.reindex)

lemma setsum_cong:
  "A = B ==> (!!x. x:B ==> f x = g x) ==> setsum f A = setsum g B"
  by (fact setsum.cong)

lemma strong_setsum_cong:
  "A = B ==> (!!x. x:B =simp=> f x = g x)
   ==> setsum (%x. f x) A = setsum (%x. g x) B"
  by (fact setsum.strong_cong)

lemmas setsum_0 = setsum.neutral_const
lemmas setsum_0' = setsum.neutral

lemma setsum_Un_Int: "finite A ==> finite B ==>
  setsum g (A Un B) + setsum g (A Int B) = setsum g A + setsum g B"
  -- {* The reversed orientation looks more natural, but LOOPS as a simprule! *}
  by (fact setsum.union_inter)

lemma setsum_Un_disjoint: "finite A ==> finite B
  ==> A Int B = {} ==> setsum g (A Un B) = setsum g A + setsum g B"
  by (fact setsum.union_disjoint)

lemma setsum_subset_diff: "\<lbrakk> B \<subseteq> A; finite A \<rbrakk> \<Longrightarrow>
    setsum f A = setsum f (A - B) + setsum f B"
  by (fact setsum.subset_diff)

lemma setsum_mono_zero_left: 
  "\<lbrakk> finite T; S \<subseteq> T; \<forall>i \<in> T - S. f i = 0 \<rbrakk> \<Longrightarrow> setsum f S = setsum f T"
  by (fact setsum.mono_neutral_left)

lemmas setsum_mono_zero_right = setsum.mono_neutral_right

lemma setsum_mono_zero_cong_left: 
  "\<lbrakk> finite T; S \<subseteq> T; \<forall>i \<in> T - S. g i = 0; \<And>x. x \<in> S \<Longrightarrow> f x = g x \<rbrakk>
  \<Longrightarrow> setsum f S = setsum g T"
  by (fact setsum.mono_neutral_cong_left)

lemmas setsum_mono_zero_cong_right = setsum.mono_neutral_cong_right

lemma setsum_delta: "finite S \<Longrightarrow>
  setsum (\<lambda>k. if k=a then b k else 0) S = (if a \<in> S then b a else 0)"
  by (fact setsum.delta)

lemma setsum_delta': "finite S \<Longrightarrow>
  setsum (\<lambda>k. if a = k then b k else 0) S = (if a\<in> S then b a else 0)"
  by (fact setsum.delta')

lemma setsum_cases:
  assumes "finite A"
  shows "setsum (\<lambda>x. if P x then f x else g x) A =
         setsum f (A \<inter> {x. P x}) + setsum g (A \<inter> - {x. P x})"
  using assms by (fact setsum.If_cases)

(*But we can't get rid of finite I. If infinite, although the rhs is 0, 
  the lhs need not be, since UNION I A could still be finite.*)
lemma setsum_UN_disjoint:
  assumes "finite I" and "ALL i:I. finite (A i)"
    and "ALL i:I. ALL j:I. i \<noteq> j --> A i Int A j = {}"
  shows "setsum f (UNION I A) = (\<Sum>i\<in>I. setsum f (A i))"
  using assms by (fact setsum.UNION_disjoint)

(*But we can't get rid of finite A. If infinite, although the lhs is 0, 
  the rhs need not be, since SIGMA A B could still be finite.*)
lemma setsum_Sigma:
  assumes "finite A" and  "ALL x:A. finite (B x)"
  shows "(\<Sum>x\<in>A. (\<Sum>y\<in>B x. f x y)) = (\<Sum>(x,y)\<in>(SIGMA x:A. B x). f x y)"
  using assms by (fact setsum.Sigma)

lemma setsum_addf: "setsum (%x. f x + g x) A = (setsum f A + setsum g A)"
  by (fact setsum.distrib)

lemma setsum_Un_zero:  
  "\<lbrakk> finite S; finite T; \<forall>x \<in> S\<inter>T. f x = 0 \<rbrakk> \<Longrightarrow>
  setsum f (S \<union> T) = setsum f S + setsum f T"
  by (fact setsum.union_inter_neutral)

lemma setsum_eq_general_reverses:
  assumes fS: "finite S" and fT: "finite T"
  and kh: "\<And>y. y \<in> T \<Longrightarrow> k y \<in> S \<and> h (k y) = y"
  and hk: "\<And>x. x \<in> S \<Longrightarrow> h x \<in> T \<and> k (h x) = x \<and> g (h x) = f x"
  shows "setsum f S = setsum g T"
  using kh hk by (fact setsum.eq_general_reverses)


subsubsection {* Properties in more restricted classes of structures *}

lemma setsum_Un: "finite A ==> finite B ==>
  (setsum f (A Un B) :: 'a :: ab_group_add) =
   setsum f A + setsum f B - setsum f (A Int B)"
by (subst setsum_Un_Int [symmetric], auto simp add: algebra_simps)

lemma setsum_Un2:
  assumes "finite (A \<union> B)"
  shows "setsum f (A \<union> B) = setsum f (A - B) + setsum f (B - A) + setsum f (A \<inter> B)"
proof -
  have "A \<union> B = A - B \<union> (B - A) \<union> A \<inter> B"
    by auto
  with assms show ?thesis by simp (subst setsum_Un_disjoint, auto)+
qed

lemma setsum_diff1: "finite A \<Longrightarrow>
  (setsum f (A - {a}) :: ('a::ab_group_add)) =
  (if a:A then setsum f A - f a else setsum f A)"
by (erule finite_induct) (auto simp add: insert_Diff_if)

lemma setsum_diff:
  assumes le: "finite A" "B \<subseteq> A"
  shows "setsum f (A - B) = setsum f A - ((setsum f B)::('a::ab_group_add))"
proof -
  from le have finiteB: "finite B" using finite_subset by auto
  show ?thesis using finiteB le
  proof induct
    case empty
    thus ?case by auto
  next
    case (insert x F)
    thus ?case using le finiteB 
      by (simp add: Diff_insert[where a=x and B=F] setsum_diff1 insert_absorb)
  qed
qed

lemma setsum_mono:
  assumes le: "\<And>i. i\<in>K \<Longrightarrow> f (i::'a) \<le> ((g i)::('b::{comm_monoid_add, ordered_ab_semigroup_add}))"
  shows "(\<Sum>i\<in>K. f i) \<le> (\<Sum>i\<in>K. g i)"
proof (cases "finite K")
  case True
  thus ?thesis using le
  proof induct
    case empty
    thus ?case by simp
  next
    case insert
    thus ?case using add_mono by fastforce
  qed
next
  case False then show ?thesis by simp
qed

lemma setsum_strict_mono:
  fixes f :: "'a \<Rightarrow> 'b::{ordered_cancel_ab_semigroup_add,comm_monoid_add}"
  assumes "finite A"  "A \<noteq> {}"
    and "!!x. x:A \<Longrightarrow> f x < g x"
  shows "setsum f A < setsum g A"
  using assms
proof (induct rule: finite_ne_induct)
  case singleton thus ?case by simp
next
  case insert thus ?case by (auto simp: add_strict_mono)
qed

lemma setsum_strict_mono_ex1:
fixes f :: "'a \<Rightarrow> 'b::{comm_monoid_add, ordered_cancel_ab_semigroup_add}"
assumes "finite A" and "ALL x:A. f x \<le> g x" and "EX a:A. f a < g a"
shows "setsum f A < setsum g A"
proof-
  from assms(3) obtain a where a: "a:A" "f a < g a" by blast
  have "setsum f A = setsum f ((A-{a}) \<union> {a})"
    by(simp add:insert_absorb[OF `a:A`])
  also have "\<dots> = setsum f (A-{a}) + setsum f {a}"
    using `finite A` by(subst setsum_Un_disjoint) auto
  also have "setsum f (A-{a}) \<le> setsum g (A-{a})"
    by(rule setsum_mono)(simp add: assms(2))
  also have "setsum f {a} < setsum g {a}" using a by simp
  also have "setsum g (A - {a}) + setsum g {a} = setsum g((A-{a}) \<union> {a})"
    using `finite A` by(subst setsum_Un_disjoint[symmetric]) auto
  also have "\<dots> = setsum g A" by(simp add:insert_absorb[OF `a:A`])
  finally show ?thesis by (auto simp add: add_right_mono add_strict_left_mono)
qed

lemma setsum_negf:
  "setsum (%x. - (f x)::'a::ab_group_add) A = - setsum f A"
proof (cases "finite A")
  case True thus ?thesis by (induct set: finite) auto
next
  case False thus ?thesis by simp
qed

lemma setsum_subtractf:
  "setsum (%x. ((f x)::'a::ab_group_add) - g x) A =
    setsum f A - setsum g A"
  using setsum_addf [of f "- g" A] by (simp add: setsum_negf)

lemma setsum_nonneg:
  assumes nn: "\<forall>x\<in>A. (0::'a::{ordered_ab_semigroup_add,comm_monoid_add}) \<le> f x"
  shows "0 \<le> setsum f A"
proof (cases "finite A")
  case True thus ?thesis using nn
  proof induct
    case empty then show ?case by simp
  next
    case (insert x F)
    then have "0 + 0 \<le> f x + setsum f F" by (blast intro: add_mono)
    with insert show ?case by simp
  qed
next
  case False thus ?thesis by simp
qed

lemma setsum_nonpos:
  assumes np: "\<forall>x\<in>A. f x \<le> (0::'a::{ordered_ab_semigroup_add,comm_monoid_add})"
  shows "setsum f A \<le> 0"
proof (cases "finite A")
  case True thus ?thesis using np
  proof induct
    case empty then show ?case by simp
  next
    case (insert x F)
    then have "f x + setsum f F \<le> 0 + 0" by (blast intro: add_mono)
    with insert show ?case by simp
  qed
next
  case False thus ?thesis by simp
qed

lemma setsum_nonneg_leq_bound:
  fixes f :: "'a \<Rightarrow> 'b::{ordered_ab_group_add}"
  assumes "finite s" "\<And>i. i \<in> s \<Longrightarrow> f i \<ge> 0" "(\<Sum>i \<in> s. f i) = B" "i \<in> s"
  shows "f i \<le> B"
proof -
  have "0 \<le> (\<Sum> i \<in> s - {i}. f i)" and "0 \<le> f i"
    using assms by (auto intro!: setsum_nonneg)
  moreover
  have "(\<Sum> i \<in> s - {i}. f i) + f i = B"
    using assms by (simp add: setsum_diff1)
  ultimately show ?thesis by auto
qed

lemma setsum_nonneg_0:
  fixes f :: "'a \<Rightarrow> 'b::{ordered_ab_group_add}"
  assumes "finite s" and pos: "\<And> i. i \<in> s \<Longrightarrow> f i \<ge> 0"
  and "(\<Sum> i \<in> s. f i) = 0" and i: "i \<in> s"
  shows "f i = 0"
  using setsum_nonneg_leq_bound[OF assms] pos[OF i] by auto

lemma setsum_mono2:
fixes f :: "'a \<Rightarrow> 'b :: ordered_comm_monoid_add"
assumes fin: "finite B" and sub: "A \<subseteq> B" and nn: "\<And>b. b \<in> B-A \<Longrightarrow> 0 \<le> f b"
shows "setsum f A \<le> setsum f B"
proof -
  have "setsum f A \<le> setsum f A + setsum f (B-A)"
    by(simp add: add_increasing2[OF setsum_nonneg] nn Ball_def)
  also have "\<dots> = setsum f (A \<union> (B-A))" using fin finite_subset[OF sub fin]
    by (simp add:setsum_Un_disjoint del:Un_Diff_cancel)
  also have "A \<union> (B-A) = B" using sub by blast
  finally show ?thesis .
qed

lemma setsum_mono3: "finite B ==> A <= B ==> 
    ALL x: B - A. 
      0 <= ((f x)::'a::{comm_monoid_add,ordered_ab_semigroup_add}) ==>
        setsum f A <= setsum f B"
  apply (subgoal_tac "setsum f B = setsum f A + setsum f (B - A)")
  apply (erule ssubst)
  apply (subgoal_tac "setsum f A + 0 <= setsum f A + setsum f (B - A)")
  apply simp
  apply (rule add_left_mono)
  apply (erule setsum_nonneg)
  apply (subst setsum_Un_disjoint [THEN sym])
  apply (erule finite_subset, assumption)
  apply (rule finite_subset)
  prefer 2
  apply assumption
  apply (auto simp add: sup_absorb2)
done

lemma setsum_right_distrib: 
  fixes f :: "'a => ('b::semiring_0)"
  shows "r * setsum f A = setsum (%n. r * f n) A"
proof (cases "finite A")
  case True
  thus ?thesis
  proof induct
    case empty thus ?case by simp
  next
    case (insert x A) thus ?case by (simp add: distrib_left)
  qed
next
  case False thus ?thesis by simp
qed

lemma setsum_left_distrib:
  "setsum f A * (r::'a::semiring_0) = (\<Sum>n\<in>A. f n * r)"
proof (cases "finite A")
  case True
  then show ?thesis
  proof induct
    case empty thus ?case by simp
  next
    case (insert x A) thus ?case by (simp add: distrib_right)
  qed
next
  case False thus ?thesis by simp
qed

lemma setsum_divide_distrib:
  "setsum f A / (r::'a::field) = (\<Sum>n\<in>A. f n / r)"
proof (cases "finite A")
  case True
  then show ?thesis
  proof induct
    case empty thus ?case by simp
  next
    case (insert x A) thus ?case by (simp add: add_divide_distrib)
  qed
next
  case False thus ?thesis by simp
qed

lemma setsum_abs[iff]: 
  fixes f :: "'a => ('b::ordered_ab_group_add_abs)"
  shows "abs (setsum f A) \<le> setsum (%i. abs(f i)) A"
proof (cases "finite A")
  case True
  thus ?thesis
  proof induct
    case empty thus ?case by simp
  next
    case (insert x A)
    thus ?case by (auto intro: abs_triangle_ineq order_trans)
  qed
next
  case False thus ?thesis by simp
qed

lemma setsum_abs_ge_zero[iff]: 
  fixes f :: "'a => ('b::ordered_ab_group_add_abs)"
  shows "0 \<le> setsum (%i. abs(f i)) A"
proof (cases "finite A")
  case True
  thus ?thesis
  proof induct
    case empty thus ?case by simp
  next
    case (insert x A) thus ?case by auto
  qed
next
  case False thus ?thesis by simp
qed

lemma abs_setsum_abs[simp]: 
  fixes f :: "'a => ('b::ordered_ab_group_add_abs)"
  shows "abs (\<Sum>a\<in>A. abs(f a)) = (\<Sum>a\<in>A. abs(f a))"
proof (cases "finite A")
  case True
  thus ?thesis
  proof induct
    case empty thus ?case by simp
  next
    case (insert a A)
    hence "\<bar>\<Sum>a\<in>insert a A. \<bar>f a\<bar>\<bar> = \<bar>\<bar>f a\<bar> + (\<Sum>a\<in>A. \<bar>f a\<bar>)\<bar>" by simp
    also have "\<dots> = \<bar>\<bar>f a\<bar> + \<bar>\<Sum>a\<in>A. \<bar>f a\<bar>\<bar>\<bar>"  using insert by simp
    also have "\<dots> = \<bar>f a\<bar> + \<bar>\<Sum>a\<in>A. \<bar>f a\<bar>\<bar>"
      by (simp del: abs_of_nonneg)
    also have "\<dots> = (\<Sum>a\<in>insert a A. \<bar>f a\<bar>)" using insert by simp
    finally show ?case .
  qed
next
  case False thus ?thesis by simp
qed

lemma setsum_diff1'[rule_format]:
  "finite A \<Longrightarrow> a \<in> A \<longrightarrow> (\<Sum> x \<in> A. f x) = f a + (\<Sum> x \<in> (A - {a}). f x)"
apply (erule finite_induct[where F=A and P="% A. (a \<in> A \<longrightarrow> (\<Sum> x \<in> A. f x) = f a + (\<Sum> x \<in> (A - {a}). f x))"])
apply (auto simp add: insert_Diff_if add_ac)
done

lemma setsum_diff1_ring: assumes "finite A" "a \<in> A"
  shows "setsum f (A - {a}) = setsum f A - (f a::'a::ring)"
unfolding setsum_diff1'[OF assms] by auto

lemma setsum_product:
  fixes f :: "'a => ('b::semiring_0)"
  shows "setsum f A * setsum g B = (\<Sum>i\<in>A. \<Sum>j\<in>B. f i * g j)"
  by (simp add: setsum_right_distrib setsum_left_distrib) (rule setsum_commute)

lemma setsum_mult_setsum_if_inj:
fixes f :: "'a => ('b::semiring_0)"
shows "inj_on (%(a,b). f a * g b) (A \<times> B) ==>
  setsum f A * setsum g B = setsum id {f a * g b|a b. a:A & b:B}"
by(auto simp: setsum_product setsum_cartesian_product
        intro!:  setsum_reindex_cong[symmetric])

lemma setsum_SucD: "setsum f A = Suc n ==> EX a:A. 0 < f a"
apply (case_tac "finite A")
 prefer 2 apply simp
apply (erule rev_mp)
apply (erule finite_induct, auto)
done

lemma setsum_eq_0_iff [simp]:
  "finite F ==> (setsum f F = 0) = (ALL a:F. f a = (0::nat))"
  by (induct set: finite) auto

lemma setsum_eq_Suc0_iff: "finite A \<Longrightarrow>
  setsum f A = Suc 0 \<longleftrightarrow> (EX a:A. f a = Suc 0 & (ALL b:A. a\<noteq>b \<longrightarrow> f b = 0))"
apply(erule finite_induct)
apply (auto simp add:add_is_1)
done

lemmas setsum_eq_1_iff = setsum_eq_Suc0_iff[simplified One_nat_def[symmetric]]

lemma setsum_Un_nat: "finite A ==> finite B ==>
  (setsum f (A Un B) :: nat) = setsum f A + setsum f B - setsum f (A Int B)"
  -- {* For the natural numbers, we have subtraction. *}
by (subst setsum_Un_Int [symmetric], auto simp add: algebra_simps)

lemma setsum_diff1_nat: "(setsum f (A - {a}) :: nat) =
  (if a:A then setsum f A - f a else setsum f A)"
apply (case_tac "finite A")
 prefer 2 apply simp
apply (erule finite_induct)
 apply (auto simp add: insert_Diff_if)
apply (drule_tac a = a in mk_disjoint_insert, auto)
done

lemma setsum_diff_nat: 
assumes "finite B" and "B \<subseteq> A"
shows "(setsum f (A - B) :: nat) = (setsum f A) - (setsum f B)"
using assms
proof induct
  show "setsum f (A - {}) = (setsum f A) - (setsum f {})" by simp
next
  fix F x assume finF: "finite F" and xnotinF: "x \<notin> F"
    and xFinA: "insert x F \<subseteq> A"
    and IH: "F \<subseteq> A \<Longrightarrow> setsum f (A - F) = setsum f A - setsum f F"
  from xnotinF xFinA have xinAF: "x \<in> (A - F)" by simp
  from xinAF have A: "setsum f ((A - F) - {x}) = setsum f (A - F) - f x"
    by (simp add: setsum_diff1_nat)
  from xFinA have "F \<subseteq> A" by simp
  with IH have "setsum f (A - F) = setsum f A - setsum f F" by simp
  with A have B: "setsum f ((A - F) - {x}) = setsum f A - setsum f F - f x"
    by simp
  from xnotinF have "A - insert x F = (A - F) - {x}" by auto
  with B have C: "setsum f (A - insert x F) = setsum f A - setsum f F - f x"
    by simp
  from finF xnotinF have "setsum f (insert x F) = setsum f F + f x" by simp
  with C have "setsum f (A - insert x F) = setsum f A - setsum f (insert x F)"
    by simp
  thus "setsum f (A - insert x F) = setsum f A - setsum f (insert x F)" by simp
qed

lemma setsum_comp_morphism:
  assumes "h 0 = 0" and "\<And>x y. h (x + y) = h x + h y"
  shows "setsum (h \<circ> g) A = h (setsum g A)"
proof (cases "finite A")
  case False then show ?thesis by (simp add: assms)
next
  case True then show ?thesis by (induct A) (simp_all add: assms)
qed


subsubsection {* Cardinality as special case of @{const setsum} *}

lemma card_eq_setsum:
  "card A = setsum (\<lambda>x. 1) A"
proof -
  have "plus \<circ> (\<lambda>_. Suc 0) = (\<lambda>_. Suc)"
    by (simp add: fun_eq_iff)
  then have "Finite_Set.fold (plus \<circ> (\<lambda>_. Suc 0)) = Finite_Set.fold (\<lambda>_. Suc)"
    by (rule arg_cong)
  then have "Finite_Set.fold (plus \<circ> (\<lambda>_. Suc 0)) 0 A = Finite_Set.fold (\<lambda>_. Suc) 0 A"
    by (blast intro: fun_cong)
  then show ?thesis by (simp add: card.eq_fold setsum.eq_fold)
qed

lemma setsum_constant [simp]:
  "(\<Sum>x \<in> A. y) = of_nat (card A) * y"
apply (cases "finite A")
apply (erule finite_induct)
apply (auto simp add: algebra_simps)
done

lemma setsum_bounded:
  assumes le: "\<And>i. i\<in>A \<Longrightarrow> f i \<le> (K::'a::{semiring_1, ordered_ab_semigroup_add})"
  shows "setsum f A \<le> of_nat (card A) * K"
proof (cases "finite A")
  case True
  thus ?thesis using le setsum_mono[where K=A and g = "%x. K"] by simp
next
  case False thus ?thesis by simp
qed

lemma card_UN_disjoint:
  assumes "finite I" and "\<forall>i\<in>I. finite (A i)"
    and "\<forall>i\<in>I. \<forall>j\<in>I. i \<noteq> j \<longrightarrow> A i \<inter> A j = {}"
  shows "card (UNION I A) = (\<Sum>i\<in>I. card(A i))"
proof -
  have "(\<Sum>i\<in>I. card (A i)) = (\<Sum>i\<in>I. \<Sum>x\<in>A i. 1)" by simp
  with assms show ?thesis by (simp add: card_eq_setsum setsum_UN_disjoint del: setsum_constant)
qed

lemma card_Union_disjoint:
  "finite C ==> (ALL A:C. finite A) ==>
   (ALL A:C. ALL B:C. A \<noteq> B --> A Int B = {})
   ==> card (Union C) = setsum card C"
apply (frule card_UN_disjoint [of C id])
apply simp_all
done


subsubsection {* Cardinality of products *}

lemma card_SigmaI [simp]:
  "\<lbrakk> finite A; ALL a:A. finite (B a) \<rbrakk>
  \<Longrightarrow> card (SIGMA x: A. B x) = (\<Sum>a\<in>A. card (B a))"
by(simp add: card_eq_setsum setsum_Sigma del:setsum_constant)

(*
lemma SigmaI_insert: "y \<notin> A ==>
  (SIGMA x:(insert y A). B x) = (({y} <*> (B y)) \<union> (SIGMA x: A. B x))"
  by auto
*)

lemma card_cartesian_product: "card (A <*> B) = card(A) * card(B)"
  by (cases "finite A \<and> finite B")
    (auto simp add: card_eq_0_iff dest: finite_cartesian_productD1 finite_cartesian_productD2)

lemma card_cartesian_product_singleton:  "card({x} <*> A) = card(A)"
by (simp add: card_cartesian_product)


subsection {* Generalized product over a set *}

context comm_monoid_mult
begin

definition setprod :: "('b \<Rightarrow> 'a) \<Rightarrow> 'b set \<Rightarrow> 'a"
where
  "setprod = comm_monoid_set.F times 1"

sublocale setprod!: comm_monoid_set times 1
where
  "comm_monoid_set.F times 1 = setprod"
proof -
  show "comm_monoid_set times 1" ..
  then interpret setprod!: comm_monoid_set times 1 .
  from setprod_def show "comm_monoid_set.F times 1 = setprod" by rule
qed

abbreviation
  Setprod ("\<Prod>_" [1000] 999) where
  "\<Prod>A \<equiv> setprod (\<lambda>x. x) A"

end

syntax
  "_setprod" :: "pttrn => 'a set => 'b => 'b::comm_monoid_mult"  ("(3PROD _:_. _)" [0, 51, 10] 10)
syntax (xsymbols)
  "_setprod" :: "pttrn => 'a set => 'b => 'b::comm_monoid_mult"  ("(3\<Prod>_\<in>_. _)" [0, 51, 10] 10)
syntax (HTML output)
  "_setprod" :: "pttrn => 'a set => 'b => 'b::comm_monoid_mult"  ("(3\<Prod>_\<in>_. _)" [0, 51, 10] 10)

translations -- {* Beware of argument permutation! *}
  "PROD i:A. b" == "CONST setprod (%i. b) A" 
  "\<Prod>i\<in>A. b" == "CONST setprod (%i. b) A" 

text{* Instead of @{term"\<Prod>x\<in>{x. P}. e"} we introduce the shorter
 @{text"\<Prod>x|P. e"}. *}

syntax
  "_qsetprod" :: "pttrn \<Rightarrow> bool \<Rightarrow> 'a \<Rightarrow> 'a" ("(3PROD _ |/ _./ _)" [0,0,10] 10)
syntax (xsymbols)
  "_qsetprod" :: "pttrn \<Rightarrow> bool \<Rightarrow> 'a \<Rightarrow> 'a" ("(3\<Prod>_ | (_)./ _)" [0,0,10] 10)
syntax (HTML output)
  "_qsetprod" :: "pttrn \<Rightarrow> bool \<Rightarrow> 'a \<Rightarrow> 'a" ("(3\<Prod>_ | (_)./ _)" [0,0,10] 10)

translations
  "PROD x|P. t" => "CONST setprod (%x. t) {x. P}"
  "\<Prod>x|P. t" => "CONST setprod (%x. t) {x. P}"

text {* TODO These are candidates for generalization *}

context comm_monoid_mult
begin

lemma setprod_reindex_id:
  "inj_on f B ==> setprod f B = setprod id (f ` B)"
  by (auto simp add: setprod.reindex)

lemma setprod_reindex_cong:
  "inj_on f A ==> B = f ` A ==> g = h \<circ> f ==> setprod h B = setprod g A"
  by (frule setprod.reindex, simp)

lemma strong_setprod_reindex_cong:
  assumes i: "inj_on f A"
  and B: "B = f ` A" and eq: "\<And>x. x \<in> A \<Longrightarrow> g x = (h \<circ> f) x"
  shows "setprod h B = setprod g A"
proof-
  have "setprod h B = setprod (h o f) A"
    by (simp add: B setprod.reindex [OF i, of h])
  then show ?thesis apply simp
    apply (rule setprod.cong)
    apply simp
    by (simp add: eq)
qed

lemma setprod_Union_disjoint:
  assumes "\<forall>A\<in>C. finite A" "\<forall>A\<in>C. \<forall>B\<in>C. A \<noteq> B \<longrightarrow> A Int B = {}" 
  shows "setprod f (Union C) = setprod (setprod f) C"
  using assms by (fact setprod.Union_disjoint)

text{*Here we can eliminate the finiteness assumptions, by cases.*}
lemma setprod_cartesian_product:
  "(\<Prod>x\<in>A. (\<Prod>y\<in> B. f x y)) = (\<Prod>(x,y)\<in>(A <*> B). f x y)"
  by (fact setprod.cartesian_product)

lemma setprod_Un2:
  assumes "finite (A \<union> B)"
  shows "setprod f (A \<union> B) = setprod f (A - B) * setprod f (B - A) * setprod f (A \<inter> B)"
proof -
  have "A \<union> B = A - B \<union> (B - A) \<union> A \<inter> B"
    by auto
  with assms show ?thesis by simp (subst setprod.union_disjoint, auto)+
qed

end

text {* TODO These are legacy *}

lemma setprod_empty: "setprod f {} = 1"
  by (fact setprod.empty)

lemma setprod_insert: "[| finite A; a \<notin> A |] ==>
    setprod f (insert a A) = f a * setprod f A"
  by (fact setprod.insert)

lemma setprod_infinite: "~ finite A ==> setprod f A = 1"
  by (fact setprod.infinite)

lemma setprod_reindex:
  "inj_on f B ==> setprod h (f ` B) = setprod (h \<circ> f) B"
  by (fact setprod.reindex)

lemma setprod_cong:
  "A = B ==> (!!x. x:B ==> f x = g x) ==> setprod f A = setprod g B"
  by (fact setprod.cong)

lemma strong_setprod_cong:
  "A = B ==> (!!x. x:B =simp=> f x = g x) ==> setprod f A = setprod g B"
  by (fact setprod.strong_cong)

lemma setprod_Un_one:
  "\<lbrakk> finite S; finite T; \<forall>x \<in> S\<inter>T. f x = 1 \<rbrakk>
  \<Longrightarrow> setprod f (S \<union> T) = setprod f S  * setprod f T"
  by (fact setprod.union_inter_neutral)

lemmas setprod_1 = setprod.neutral_const
lemmas setprod_1' = setprod.neutral

lemma setprod_Un_Int: "finite A ==> finite B
    ==> setprod g (A Un B) * setprod g (A Int B) = setprod g A * setprod g B"
  by (fact setprod.union_inter)

lemma setprod_Un_disjoint: "finite A ==> finite B
  ==> A Int B = {} ==> setprod g (A Un B) = setprod g A * setprod g B"
  by (fact setprod.union_disjoint)

lemma setprod_subset_diff: "\<lbrakk> B \<subseteq> A; finite A \<rbrakk> \<Longrightarrow>
    setprod f A = setprod f (A - B) * setprod f B"
  by (fact setprod.subset_diff)

lemma setprod_mono_one_left:
  "\<lbrakk> finite T; S \<subseteq> T; \<forall>i \<in> T - S. f i = 1 \<rbrakk> \<Longrightarrow> setprod f S = setprod f T"
  by (fact setprod.mono_neutral_left)

lemmas setprod_mono_one_right = setprod.mono_neutral_right

lemma setprod_mono_one_cong_left: 
  "\<lbrakk> finite T; S \<subseteq> T; \<forall>i \<in> T - S. g i = 1; \<And>x. x \<in> S \<Longrightarrow> f x = g x \<rbrakk>
  \<Longrightarrow> setprod f S = setprod g T"
  by (fact setprod.mono_neutral_cong_left)

lemmas setprod_mono_one_cong_right = setprod.mono_neutral_cong_right

lemma setprod_delta: "finite S \<Longrightarrow>
  setprod (\<lambda>k. if k=a then b k else 1) S = (if a \<in> S then b a else 1)"
  by (fact setprod.delta)

lemma setprod_delta': "finite S \<Longrightarrow>
  setprod (\<lambda>k. if a = k then b k else 1) S = (if a\<in> S then b a else 1)"
  by (fact setprod.delta')

lemma setprod_UN_disjoint:
    "finite I ==> (ALL i:I. finite (A i)) ==>
        (ALL i:I. ALL j:I. i \<noteq> j --> A i Int A j = {}) ==>
      setprod f (UNION I A) = setprod (%i. setprod f (A i)) I"
  by (fact setprod.UNION_disjoint)

lemma setprod_Sigma: "finite A ==> ALL x:A. finite (B x) ==>
    (\<Prod>x\<in>A. (\<Prod>y\<in> B x. f x y)) =
    (\<Prod>(x,y)\<in>(SIGMA x:A. B x). f x y)"
  by (fact setprod.Sigma)

lemma setprod_timesf: "setprod (\<lambda>x. f x * g x) A = setprod f A * setprod g A"
  by (fact setprod.distrib)


subsubsection {* Properties in more restricted classes of structures *}

lemma setprod_zero:
     "finite A ==> EX x: A. f x = (0::'a::comm_semiring_1) ==> setprod f A = 0"
apply (induct set: finite, force, clarsimp)
apply (erule disjE, auto)
done

lemma setprod_zero_iff[simp]: "finite A ==> 
  (setprod f A = (0::'a::{comm_semiring_1,no_zero_divisors})) =
  (EX x: A. f x = 0)"
by (erule finite_induct, auto simp:no_zero_divisors)

lemma setprod_Un: "finite A ==> finite B ==> (ALL x: A Int B. f x \<noteq> 0) ==>
  (setprod f (A Un B) :: 'a ::{field})
   = setprod f A * setprod f B / setprod f (A Int B)"
by (subst setprod_Un_Int [symmetric], auto)

lemma setprod_nonneg [rule_format]:
   "(ALL x: A. (0::'a::linordered_semidom) \<le> f x) --> 0 \<le> setprod f A"
by (cases "finite A", induct set: finite, simp_all)

lemma setprod_pos [rule_format]: "(ALL x: A. (0::'a::linordered_semidom) < f x)
  --> 0 < setprod f A"
by (cases "finite A", induct set: finite, simp_all)

lemma setprod_diff1: "finite A ==> f a \<noteq> 0 ==>
  (setprod f (A - {a}) :: 'a :: {field}) =
  (if a:A then setprod f A / f a else setprod f A)"
  by (erule finite_induct) (auto simp add: insert_Diff_if)

lemma setprod_inversef: 
  fixes f :: "'b \<Rightarrow> 'a::field_inverse_zero"
  shows "finite A ==> setprod (inverse \<circ> f) A = inverse (setprod f A)"
by (erule finite_induct) auto

lemma setprod_dividef:
  fixes f :: "'b \<Rightarrow> 'a::field_inverse_zero"
  shows "finite A
    ==> setprod (%x. f x / g x) A = setprod f A / setprod g A"
apply (subgoal_tac
         "setprod (%x. f x / g x) A = setprod (%x. f x * (inverse \<circ> g) x) A")
apply (erule ssubst)
apply (subst divide_inverse)
apply (subst setprod_timesf)
apply (subst setprod_inversef, assumption+, rule refl)
apply (rule setprod_cong, rule refl)
apply (subst divide_inverse, auto)
done

lemma setprod_dvd_setprod [rule_format]: 
    "(ALL x : A. f x dvd g x) \<longrightarrow> setprod f A dvd setprod g A"
  apply (cases "finite A")
  apply (induct set: finite)
  apply (auto simp add: dvd_def)
  apply (rule_tac x = "k * ka" in exI)
  apply (simp add: algebra_simps)
done

lemma setprod_dvd_setprod_subset:
  "finite B \<Longrightarrow> A <= B \<Longrightarrow> setprod f A dvd setprod f B"
  apply (subgoal_tac "setprod f B = setprod f A * setprod f (B - A)")
  apply (unfold dvd_def, blast)
  apply (subst setprod_Un_disjoint [symmetric])
  apply (auto elim: finite_subset intro: setprod_cong)
done

lemma setprod_dvd_setprod_subset2:
  "finite B \<Longrightarrow> A <= B \<Longrightarrow> ALL x : A. (f x::'a::comm_semiring_1) dvd g x \<Longrightarrow> 
      setprod f A dvd setprod g B"
  apply (rule dvd_trans)
  apply (rule setprod_dvd_setprod, erule (1) bspec)
  apply (erule (1) setprod_dvd_setprod_subset)
done

lemma dvd_setprod: "finite A \<Longrightarrow> i:A \<Longrightarrow> 
    (f i ::'a::comm_semiring_1) dvd setprod f A"
by (induct set: finite) (auto intro: dvd_mult)

lemma dvd_setsum [rule_format]: "(ALL i : A. d dvd f i) \<longrightarrow> 
    (d::'a::comm_semiring_1) dvd (SUM x : A. f x)"
  apply (cases "finite A")
  apply (induct set: finite)
  apply auto
done

lemma setprod_mono:
  fixes f :: "'a \<Rightarrow> 'b\<Colon>linordered_semidom"
  assumes "\<forall>i\<in>A. 0 \<le> f i \<and> f i \<le> g i"
  shows "setprod f A \<le> setprod g A"
proof (cases "finite A")
  case True
  hence ?thesis "setprod f A \<ge> 0" using subset_refl[of A]
  proof (induct A rule: finite_subset_induct)
    case (insert a F)
    thus "setprod f (insert a F) \<le> setprod g (insert a F)" "0 \<le> setprod f (insert a F)"
      unfolding setprod_insert[OF insert(1,3)]
      using assms[rule_format,OF insert(2)] insert
      by (auto intro: mult_mono)
  qed auto
  thus ?thesis by simp
qed auto

lemma abs_setprod:
  fixes f :: "'a \<Rightarrow> 'b\<Colon>{linordered_field,abs}"
  shows "abs (setprod f A) = setprod (\<lambda>x. abs (f x)) A"
proof (cases "finite A")
  case True thus ?thesis
    by induct (auto simp add: field_simps abs_mult)
qed auto

lemma setprod_eq_1_iff [simp]:
  "finite F ==> setprod f F = 1 \<longleftrightarrow> (ALL a:F. f a = (1::nat))"
  by (induct set: finite) auto

lemma setprod_pos_nat:
  "finite S ==> (ALL x : S. f x > (0::nat)) ==> setprod f S > 0"
using setprod_zero_iff by(simp del:neq0_conv add:neq0_conv[symmetric])

lemma setprod_pos_nat_iff[simp]:
  "finite S ==> (setprod f S > 0) = (ALL x : S. f x > (0::nat))"
using setprod_zero_iff by(simp del:neq0_conv add:neq0_conv[symmetric])

end