added lemmas image_mset_eq_{image_mset_plus,plus,plus_image_mset}D, and multp_image_mset_image_msetD
(* Title: HOL/Library/Ramsey.thy
Author: Tom Ridge. Full finite version by L C Paulson.
*)
section \<open>Ramsey's Theorem\<close>
theory Ramsey
imports Infinite_Set FuncSet
begin
subsection \<open>Preliminary definitions\<close>
abbreviation strict_sorted :: "'a::linorder list \<Rightarrow> bool" where
"strict_sorted \<equiv> sorted_wrt (<)"
subsubsection \<open>The $n$-element subsets of a set $A$\<close>
definition nsets :: "['a set, nat] \<Rightarrow> 'a set set" ("([_]\<^bsup>_\<^esup>)" [0,999] 999)
where "nsets A n \<equiv> {N. N \<subseteq> A \<and> finite N \<and> card N = n}"
lemma nsets_mono: "A \<subseteq> B \<Longrightarrow> nsets A n \<subseteq> nsets B n"
by (auto simp: nsets_def)
lemma nsets_Pi_contra: "A' \<subseteq> A \<Longrightarrow> Pi ([A]\<^bsup>n\<^esup>) B \<subseteq> Pi ([A']\<^bsup>n\<^esup>) B"
by (auto simp: nsets_def)
lemma nsets_2_eq: "nsets A 2 = (\<Union>x\<in>A. \<Union>y\<in>A - {x}. {{x, y}})"
by (auto simp: nsets_def card_2_iff)
lemma nsets_doubleton_2_eq [simp]: "[{x, y}]\<^bsup>2\<^esup> = (if x=y then {} else {{x, y}})"
by (auto simp: nsets_2_eq)
lemma doubleton_in_nsets_2 [simp]: "{x,y} \<in> [A]\<^bsup>2\<^esup> \<longleftrightarrow> x \<in> A \<and> y \<in> A \<and> x \<noteq> y"
by (auto simp: nsets_2_eq Set.doubleton_eq_iff)
lemma nsets_3_eq: "nsets A 3 = (\<Union>x\<in>A. \<Union>y\<in>A - {x}. \<Union>z\<in>A - {x,y}. {{x,y,z}})"
by (simp add: eval_nat_numeral nsets_def card_Suc_eq) blast
lemma nsets_4_eq: "[A]\<^bsup>4\<^esup> = (\<Union>u\<in>A. \<Union>x\<in>A - {u}. \<Union>y\<in>A - {u,x}. \<Union>z\<in>A - {u,x,y}. {{u,x,y,z}})"
(is "_ = ?rhs")
proof
show "[A]\<^bsup>4\<^esup> \<subseteq> ?rhs"
by (clarsimp simp add: nsets_def eval_nat_numeral card_Suc_eq) blast
show "?rhs \<subseteq> [A]\<^bsup>4\<^esup>"
apply (clarsimp simp add: nsets_def eval_nat_numeral card_Suc_eq)
by (metis insert_iff singletonD)
qed
lemma nsets_disjoint_2:
"X \<inter> Y = {} \<Longrightarrow> [X \<union> Y]\<^bsup>2\<^esup> = [X]\<^bsup>2\<^esup> \<union> [Y]\<^bsup>2\<^esup> \<union> (\<Union>x\<in>X. \<Union>y\<in>Y. {{x,y}})"
by (fastforce simp: nsets_2_eq Set.doubleton_eq_iff)
lemma ordered_nsets_2_eq:
fixes A :: "'a::linorder set"
shows "nsets A 2 = {{x,y} | x y. x \<in> A \<and> y \<in> A \<and> x<y}"
(is "_ = ?rhs")
proof
show "nsets A 2 \<subseteq> ?rhs"
unfolding numeral_nat
apply (clarsimp simp add: nsets_def card_Suc_eq Set.doubleton_eq_iff not_less)
by (metis antisym)
show "?rhs \<subseteq> nsets A 2"
unfolding numeral_nat by (auto simp: nsets_def card_Suc_eq)
qed
lemma ordered_nsets_3_eq:
fixes A :: "'a::linorder set"
shows "nsets A 3 = {{x,y,z} | x y z. x \<in> A \<and> y \<in> A \<and> z \<in> A \<and> x<y \<and> y<z}"
(is "_ = ?rhs")
proof
show "nsets A 3 \<subseteq> ?rhs"
apply (clarsimp simp add: nsets_def card_Suc_eq eval_nat_numeral)
by (metis insert_commute linorder_cases)
show "?rhs \<subseteq> nsets A 3"
apply (clarsimp simp add: nsets_def card_Suc_eq eval_nat_numeral)
by (metis empty_iff insert_iff not_less_iff_gr_or_eq)
qed
lemma ordered_nsets_4_eq:
fixes A :: "'a::linorder set"
shows "[A]\<^bsup>4\<^esup> = {U. \<exists>u x y z. U = {u,x,y,z} \<and> u \<in> A \<and> x \<in> A \<and> y \<in> A \<and> z \<in> A \<and> u < x \<and> x < y \<and> y < z}"
(is "_ = Collect ?RHS")
proof -
{ fix U
assume "U \<in> [A]\<^bsup>4\<^esup>"
then obtain l where "strict_sorted l" "List.set l = U" "length l = 4" "U \<subseteq> A"
by (simp add: nsets_def) (metis finite_set_strict_sorted)
then have "?RHS U"
unfolding numeral_nat length_Suc_conv by auto blast }
moreover
have "Collect ?RHS \<subseteq> [A]\<^bsup>4\<^esup>"
apply (clarsimp simp add: nsets_def eval_nat_numeral)
apply (subst card_insert_disjoint, auto)+
done
ultimately show ?thesis
by auto
qed
lemma ordered_nsets_5_eq:
fixes A :: "'a::linorder set"
shows "[A]\<^bsup>5\<^esup> = {U. \<exists>u v x y z. U = {u,v,x,y,z} \<and> u \<in> A \<and> v \<in> A \<and> x \<in> A \<and> y \<in> A \<and> z \<in> A \<and> u < v \<and> v < x \<and> x < y \<and> y < z}"
(is "_ = Collect ?RHS")
proof -
{ fix U
assume "U \<in> [A]\<^bsup>5\<^esup>"
then obtain l where "strict_sorted l" "List.set l = U" "length l = 5" "U \<subseteq> A"
apply (simp add: nsets_def)
by (metis finite_set_strict_sorted)
then have "?RHS U"
unfolding numeral_nat length_Suc_conv by auto blast }
moreover
have "Collect ?RHS \<subseteq> [A]\<^bsup>5\<^esup>"
apply (clarsimp simp add: nsets_def eval_nat_numeral)
apply (subst card_insert_disjoint, auto)+
done
ultimately show ?thesis
by auto
qed
lemma binomial_eq_nsets: "n choose k = card (nsets {0..<n} k)"
apply (simp add: binomial_def nsets_def)
by (meson subset_eq_atLeast0_lessThan_finite)
lemma nsets_eq_empty_iff: "nsets A r = {} \<longleftrightarrow> finite A \<and> card A < r"
unfolding nsets_def
proof (intro iffI conjI)
assume that: "{N. N \<subseteq> A \<and> finite N \<and> card N = r} = {}"
show "finite A"
using infinite_arbitrarily_large that by auto
then have "\<not> r \<le> card A"
using that by (simp add: set_eq_iff) (metis obtain_subset_with_card_n)
then show "card A < r"
using not_less by blast
next
show "{N. N \<subseteq> A \<and> finite N \<and> card N = r} = {}"
if "finite A \<and> card A < r"
using that card_mono leD by auto
qed
lemma nsets_eq_empty: "\<lbrakk>finite A; card A < r\<rbrakk> \<Longrightarrow> nsets A r = {}"
by (simp add: nsets_eq_empty_iff)
lemma nsets_empty_iff: "nsets {} r = (if r=0 then {{}} else {})"
by (auto simp: nsets_def)
lemma nsets_singleton_iff: "nsets {a} r = (if r=0 then {{}} else if r=1 then {{a}} else {})"
by (auto simp: nsets_def card_gt_0_iff subset_singleton_iff)
lemma nsets_self [simp]: "nsets {..<m} m = {{..<m}}"
unfolding nsets_def
apply auto
by (metis add.left_neutral lessThan_atLeast0 lessThan_iff subset_card_intvl_is_intvl)
lemma nsets_zero [simp]: "nsets A 0 = {{}}"
by (auto simp: nsets_def)
lemma nsets_one: "nsets A (Suc 0) = (\<lambda>x. {x}) ` A"
using card_eq_SucD by (force simp: nsets_def)
lemma inj_on_nsets:
assumes "inj_on f A"
shows "inj_on (\<lambda>X. f ` X) ([A]\<^bsup>n\<^esup>)"
using assms unfolding nsets_def
by (metis (no_types, lifting) inj_on_inverseI inv_into_image_cancel mem_Collect_eq)
lemma bij_betw_nsets:
assumes "bij_betw f A B"
shows "bij_betw (\<lambda>X. f ` X) ([A]\<^bsup>n\<^esup>) ([B]\<^bsup>n\<^esup>)"
proof -
have "(`) f ` [A]\<^bsup>n\<^esup> = [f ` A]\<^bsup>n\<^esup>"
using assms
apply (auto simp: nsets_def bij_betw_def image_iff card_image inj_on_subset)
by (metis card_image inj_on_finite order_refl subset_image_inj)
with assms show ?thesis
by (auto simp: bij_betw_def inj_on_nsets)
qed
lemma nset_image_obtains:
assumes "X \<in> [f`A]\<^bsup>k\<^esup>" "inj_on f A"
obtains Y where "Y \<in> [A]\<^bsup>k\<^esup>" "X = f ` Y"
using assms
apply (clarsimp simp add: nsets_def subset_image_iff)
by (metis card_image finite_imageD inj_on_subset)
lemma nsets_image_funcset:
assumes "g \<in> S \<rightarrow> T" and "inj_on g S"
shows "(\<lambda>X. g ` X) \<in> [S]\<^bsup>k\<^esup> \<rightarrow> [T]\<^bsup>k\<^esup>"
using assms
by (fastforce simp add: nsets_def card_image inj_on_subset subset_iff simp flip: image_subset_iff_funcset)
lemma nsets_compose_image_funcset:
assumes f: "f \<in> [T]\<^bsup>k\<^esup> \<rightarrow> D" and "g \<in> S \<rightarrow> T" and "inj_on g S"
shows "f \<circ> (\<lambda>X. g ` X) \<in> [S]\<^bsup>k\<^esup> \<rightarrow> D"
proof -
have "(\<lambda>X. g ` X) \<in> [S]\<^bsup>k\<^esup> \<rightarrow> [T]\<^bsup>k\<^esup>"
using assms by (simp add: nsets_image_funcset)
then show ?thesis
using f by fastforce
qed
subsubsection \<open>Partition predicates\<close>
definition partn :: "'a set \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> 'b set \<Rightarrow> bool"
where "partn \<beta> \<alpha> \<gamma> \<delta> \<equiv> \<forall>f \<in> nsets \<beta> \<gamma> \<rightarrow> \<delta>. \<exists>H \<in> nsets \<beta> \<alpha>. \<exists>\<xi>\<in>\<delta>. f ` (nsets H \<gamma>) \<subseteq> {\<xi>}"
definition partn_lst :: "'a set \<Rightarrow> nat list \<Rightarrow> nat \<Rightarrow> bool"
where "partn_lst \<beta> \<alpha> \<gamma> \<equiv> \<forall>f \<in> nsets \<beta> \<gamma> \<rightarrow> {..<length \<alpha>}.
\<exists>i < length \<alpha>. \<exists>H \<in> nsets \<beta> (\<alpha>!i). f ` (nsets H \<gamma>) \<subseteq> {i}"
lemma partn_lst_greater_resource:
fixes M::nat
assumes M: "partn_lst {..<M} \<alpha> \<gamma>" and "M \<le> N"
shows "partn_lst {..<N} \<alpha> \<gamma>"
proof (clarsimp simp: partn_lst_def)
fix f
assume "f \<in> nsets {..<N} \<gamma> \<rightarrow> {..<length \<alpha>}"
then have "f \<in> nsets {..<M} \<gamma> \<rightarrow> {..<length \<alpha>}"
by (meson Pi_anti_mono \<open>M \<le> N\<close> lessThan_subset_iff nsets_mono subsetD)
then obtain i H where i: "i < length \<alpha>" and H: "H \<in> nsets {..<M} (\<alpha> ! i)" and subi: "f ` nsets H \<gamma> \<subseteq> {i}"
using M partn_lst_def by blast
have "H \<in> nsets {..<N} (\<alpha> ! i)"
using \<open>M \<le> N\<close> H by (auto simp: nsets_def subset_iff)
then show "\<exists>i<length \<alpha>. \<exists>H\<in>nsets {..<N} (\<alpha> ! i). f ` nsets H \<gamma> \<subseteq> {i}"
using i subi by blast
qed
lemma partn_lst_fewer_colours:
assumes major: "partn_lst \<beta> (n#\<alpha>) \<gamma>" and "n \<ge> \<gamma>"
shows "partn_lst \<beta> \<alpha> \<gamma>"
proof (clarsimp simp: partn_lst_def)
fix f :: "'a set \<Rightarrow> nat"
assume f: "f \<in> [\<beta>]\<^bsup>\<gamma>\<^esup> \<rightarrow> {..<length \<alpha>}"
then obtain i H where i: "i < Suc (length \<alpha>)"
and H: "H \<in> [\<beta>]\<^bsup>((n # \<alpha>) ! i)\<^esup>"
and hom: "\<forall>x\<in>[H]\<^bsup>\<gamma>\<^esup>. Suc (f x) = i"
using \<open>n \<ge> \<gamma>\<close> major [unfolded partn_lst_def, rule_format, of "Suc o f"]
by (fastforce simp: image_subset_iff nsets_eq_empty_iff)
show "\<exists>i<length \<alpha>. \<exists>H\<in>nsets \<beta> (\<alpha> ! i). f ` [H]\<^bsup>\<gamma>\<^esup> \<subseteq> {i}"
proof (cases i)
case 0
then have "[H]\<^bsup>\<gamma>\<^esup> = {}"
using hom by blast
then show ?thesis
using 0 H \<open>n \<ge> \<gamma>\<close>
by (simp add: nsets_eq_empty_iff) (simp add: nsets_def)
next
case (Suc i')
then show ?thesis
using i H hom by auto
qed
qed
lemma partn_lst_eq_partn: "partn_lst {..<n} [m,m] 2 = partn {..<n} m 2 {..<2::nat}"
apply (simp add: partn_lst_def partn_def numeral_2_eq_2)
by (metis less_2_cases numeral_2_eq_2 lessThan_iff nth_Cons_0 nth_Cons_Suc)
subsection \<open>Finite versions of Ramsey's theorem\<close>
text \<open>
To distinguish the finite and infinite ones, lower and upper case
names are used.
\<close>
subsubsection \<open>Trivial cases\<close>
text \<open>Vacuous, since we are dealing with 0-sets!\<close>
lemma ramsey0: "\<exists>N::nat. partn_lst {..<N} [q1,q2] 0"
by (force simp: partn_lst_def ex_in_conv less_Suc_eq nsets_eq_empty_iff)
text \<open>Just the pigeon hole principle, since we are dealing with 1-sets\<close>
lemma ramsey1: "\<exists>N::nat. partn_lst {..<N} [q0,q1] 1"
proof -
have "\<exists>i<Suc (Suc 0). \<exists>H\<in>nsets {..<Suc (q0 + q1)} ([q0, q1] ! i). f ` nsets H (Suc 0) \<subseteq> {i}"
if "f \<in> nsets {..<Suc (q0 + q1)} (Suc 0) \<rightarrow> {..<Suc (Suc 0)}" for f
proof -
define A where "A \<equiv> \<lambda>i. {q. q \<le> q0+q1 \<and> f {q} = i}"
have "A 0 \<union> A 1 = {..q0 + q1}"
using that by (auto simp: A_def PiE_iff nsets_one lessThan_Suc_atMost le_Suc_eq)
moreover have "A 0 \<inter> A 1 = {}"
by (auto simp: A_def)
ultimately have "q0 + q1 \<le> card (A 0) + card (A 1)"
by (metis card_Un_le card_atMost eq_imp_le le_SucI le_trans)
then consider "card (A 0) \<ge> q0" | "card (A 1) \<ge> q1"
by linarith
then obtain i where "i < Suc (Suc 0)" "card (A i) \<ge> [q0, q1] ! i"
by (metis One_nat_def lessI nth_Cons_0 nth_Cons_Suc zero_less_Suc)
then obtain B where "B \<subseteq> A i" "card B = [q0, q1] ! i" "finite B"
by (meson obtain_subset_with_card_n)
then have "B \<in> nsets {..<Suc (q0 + q1)} ([q0, q1] ! i) \<and> f ` nsets B (Suc 0) \<subseteq> {i}"
by (auto simp: A_def nsets_def card_1_singleton_iff)
then show ?thesis
using \<open>i < Suc (Suc 0)\<close> by auto
qed
then show ?thesis
by (clarsimp simp: partn_lst_def) blast
qed
subsubsection \<open>Ramsey's theorem with two colours and arbitrary exponents (hypergraph version)\<close>
proposition ramsey2_full: "\<exists>N::nat. partn_lst {..<N} [q1,q2] r"
proof (induction r arbitrary: q1 q2)
case 0
then show ?case
by (simp add: ramsey0)
next
case (Suc r)
note outer = this
show ?case
proof (cases "r = 0")
case True
then show ?thesis
using ramsey1 by auto
next
case False
then have "r > 0"
by simp
show ?thesis
using Suc.prems
proof (induct k \<equiv> "q1 + q2" arbitrary: q1 q2)
case 0
show ?case
proof
show "partn_lst {..<1::nat} [q1, q2] (Suc r)"
using nsets_empty_iff subset_insert 0
by (fastforce simp: partn_lst_def funcset_to_empty_iff nsets_eq_empty image_subset_iff)
qed
next
case (Suc k)
consider "q1 = 0 \<or> q2 = 0" | "q1 \<noteq> 0" "q2 \<noteq> 0" by auto
then show ?case
proof cases
case 1
then have "partn_lst {..< Suc 0} [q1, q2] (Suc r)"
unfolding partn_lst_def using \<open>r > 0\<close>
by (fastforce simp add: nsets_empty_iff nsets_singleton_iff lessThan_Suc)
then show ?thesis by blast
next
case 2
with Suc have "k = (q1 - 1) + q2" "k = q1 + (q2 - 1)" by auto
then obtain p1 p2::nat where p1: "partn_lst {..<p1} [q1-1,q2] (Suc r)" and p2: "partn_lst {..<p2} [q1,q2-1] (Suc r)"
using Suc.hyps by blast
then obtain p::nat where p: "partn_lst {..<p} [p1,p2] r"
using outer Suc.prems by auto
show ?thesis
proof (intro exI conjI)
have "\<exists>i<Suc (Suc 0). \<exists>H\<in>nsets {..p} ([q1,q2] ! i). f ` nsets H (Suc r) \<subseteq> {i}"
if f: "f \<in> nsets {..p} (Suc r) \<rightarrow> {..<Suc (Suc 0)}" for f
proof -
define g where "g \<equiv> \<lambda>R. f (insert p R)"
have "f (insert p i) \<in> {..<Suc (Suc 0)}" if "i \<in> nsets {..<p} r" for i
using that card_insert_if by (fastforce simp: nsets_def intro!: Pi_mem [OF f])
then have g: "g \<in> nsets {..<p} r \<rightarrow> {..<Suc (Suc 0)}"
by (force simp: g_def PiE_iff)
then obtain i U where i: "i < Suc (Suc 0)" and gi: "g ` nsets U r \<subseteq> {i}"
and U: "U \<in> nsets {..<p} ([p1, p2] ! i)"
using p by (auto simp: partn_lst_def)
then have Usub: "U \<subseteq> {..<p}"
by (auto simp: nsets_def)
consider (izero) "i = 0" | (ione) "i = Suc 0"
using i by linarith
then show ?thesis
proof cases
case izero
then have "U \<in> nsets {..<p} p1"
using U by simp
then obtain u where u: "bij_betw u {..<p1} U"
using ex_bij_betw_nat_finite lessThan_atLeast0 by (fastforce simp add: nsets_def)
have u_nsets: "u ` X \<in> nsets {..p} n" if "X \<in> nsets {..<p1} n" for X n
proof -
have "inj_on u X"
using u that bij_betw_imp_inj_on inj_on_subset by (force simp: nsets_def)
then show ?thesis
using Usub u that bij_betwE
by (fastforce simp add: nsets_def card_image)
qed
define h where "h \<equiv> \<lambda>R. f (u ` R)"
have "h \<in> nsets {..<p1} (Suc r) \<rightarrow> {..<Suc (Suc 0)}"
unfolding h_def using f u_nsets by auto
then obtain j V where j: "j <Suc (Suc 0)" and hj: "h ` nsets V (Suc r) \<subseteq> {j}"
and V: "V \<in> nsets {..<p1} ([q1 - Suc 0, q2] ! j)"
using p1 by (auto simp: partn_lst_def)
then have Vsub: "V \<subseteq> {..<p1}"
by (auto simp: nsets_def)
have invinv_eq: "u ` inv_into {..<p1} u ` X = X" if "X \<subseteq> u ` {..<p1}" for X
by (simp add: image_inv_into_cancel that)
let ?W = "insert p (u ` V)"
consider (jzero) "j = 0" | (jone) "j = Suc 0"
using j by linarith
then show ?thesis
proof cases
case jzero
then have "V \<in> nsets {..<p1} (q1 - Suc 0)"
using V by simp
then have "u ` V \<in> nsets {..<p} (q1 - Suc 0)"
using u_nsets [of _ "q1 - Suc 0"] nsets_mono [OF Vsub] Usub u
unfolding bij_betw_def nsets_def
by (fastforce elim!: subsetD)
then have inq1: "?W \<in> nsets {..p} q1"
unfolding nsets_def using \<open>q1 \<noteq> 0\<close> card_insert_if by fastforce
have invu_nsets: "inv_into {..<p1} u ` X \<in> nsets V r"
if "X \<in> nsets (u ` V) r" for X r
proof -
have "X \<subseteq> u ` V \<and> finite X \<and> card X = r"
using nsets_def that by auto
then have [simp]: "card (inv_into {..<p1} u ` X) = card X"
by (meson Vsub bij_betw_def bij_betw_inv_into card_image image_mono inj_on_subset u)
show ?thesis
using that u Vsub by (fastforce simp: nsets_def bij_betw_def)
qed
have "f X = i" if X: "X \<in> nsets ?W (Suc r)" for X
proof (cases "p \<in> X")
case True
then have Xp: "X - {p} \<in> nsets (u ` V) r"
using X by (auto simp: nsets_def)
moreover have "u ` V \<subseteq> U"
using Vsub bij_betwE u by blast
ultimately have "X - {p} \<in> nsets U r"
by (meson in_mono nsets_mono)
then have "g (X - {p}) = i"
using gi by blast
have "f X = i"
using gi True \<open>X - {p} \<in> nsets U r\<close> insert_Diff
by (fastforce simp add: g_def image_subset_iff)
then show ?thesis
by (simp add: \<open>f X = i\<close> \<open>g (X - {p}) = i\<close>)
next
case False
then have Xim: "X \<in> nsets (u ` V) (Suc r)"
using X by (auto simp: nsets_def subset_insert)
then have "u ` inv_into {..<p1} u ` X = X"
using Vsub bij_betw_imp_inj_on u
by (fastforce simp: nsets_def image_mono invinv_eq subset_trans)
then show ?thesis
using izero jzero hj Xim invu_nsets unfolding h_def
by (fastforce simp add: image_subset_iff)
qed
moreover have "insert p (u ` V) \<in> nsets {..p} q1"
by (simp add: izero inq1)
ultimately show ?thesis
by (metis izero image_subsetI insertI1 nth_Cons_0 zero_less_Suc)
next
case jone
then have "u ` V \<in> nsets {..p} q2"
using V u_nsets by auto
moreover have "f ` nsets (u ` V) (Suc r) \<subseteq> {j}"
using hj
by (force simp add: h_def image_subset_iff nsets_def subset_image_inj card_image dest: finite_imageD)
ultimately show ?thesis
using jone not_less_eq by fastforce
qed
next
case ione
then have "U \<in> nsets {..<p} p2"
using U by simp
then obtain u where u: "bij_betw u {..<p2} U"
using ex_bij_betw_nat_finite lessThan_atLeast0 by (fastforce simp add: nsets_def)
have u_nsets: "u ` X \<in> nsets {..p} n" if "X \<in> nsets {..<p2} n" for X n
proof -
have "inj_on u X"
using u that bij_betw_imp_inj_on inj_on_subset by (force simp: nsets_def)
then show ?thesis
using Usub u that bij_betwE
by (fastforce simp add: nsets_def card_image)
qed
define h where "h \<equiv> \<lambda>R. f (u ` R)"
have "h \<in> nsets {..<p2} (Suc r) \<rightarrow> {..<Suc (Suc 0)}"
unfolding h_def using f u_nsets by auto
then obtain j V where j: "j <Suc (Suc 0)" and hj: "h ` nsets V (Suc r) \<subseteq> {j}"
and V: "V \<in> nsets {..<p2} ([q1, q2 - Suc 0] ! j)"
using p2 by (auto simp: partn_lst_def)
then have Vsub: "V \<subseteq> {..<p2}"
by (auto simp: nsets_def)
have invinv_eq: "u ` inv_into {..<p2} u ` X = X" if "X \<subseteq> u ` {..<p2}" for X
by (simp add: image_inv_into_cancel that)
let ?W = "insert p (u ` V)"
consider (jzero) "j = 0" | (jone) "j = Suc 0"
using j by linarith
then show ?thesis
proof cases
case jone
then have "V \<in> nsets {..<p2} (q2 - Suc 0)"
using V by simp
then have "u ` V \<in> nsets {..<p} (q2 - Suc 0)"
using u_nsets [of _ "q2 - Suc 0"] nsets_mono [OF Vsub] Usub u
unfolding bij_betw_def nsets_def
by (fastforce elim!: subsetD)
then have inq1: "?W \<in> nsets {..p} q2"
unfolding nsets_def using \<open>q2 \<noteq> 0\<close> card_insert_if by fastforce
have invu_nsets: "inv_into {..<p2} u ` X \<in> nsets V r"
if "X \<in> nsets (u ` V) r" for X r
proof -
have "X \<subseteq> u ` V \<and> finite X \<and> card X = r"
using nsets_def that by auto
then have [simp]: "card (inv_into {..<p2} u ` X) = card X"
by (meson Vsub bij_betw_def bij_betw_inv_into card_image image_mono inj_on_subset u)
show ?thesis
using that u Vsub by (fastforce simp: nsets_def bij_betw_def)
qed
have "f X = i" if X: "X \<in> nsets ?W (Suc r)" for X
proof (cases "p \<in> X")
case True
then have Xp: "X - {p} \<in> nsets (u ` V) r"
using X by (auto simp: nsets_def)
moreover have "u ` V \<subseteq> U"
using Vsub bij_betwE u by blast
ultimately have "X - {p} \<in> nsets U r"
by (meson in_mono nsets_mono)
then have "g (X - {p}) = i"
using gi by blast
have "f X = i"
using gi True \<open>X - {p} \<in> nsets U r\<close> insert_Diff
by (fastforce simp add: g_def image_subset_iff)
then show ?thesis
by (simp add: \<open>f X = i\<close> \<open>g (X - {p}) = i\<close>)
next
case False
then have Xim: "X \<in> nsets (u ` V) (Suc r)"
using X by (auto simp: nsets_def subset_insert)
then have "u ` inv_into {..<p2} u ` X = X"
using Vsub bij_betw_imp_inj_on u
by (fastforce simp: nsets_def image_mono invinv_eq subset_trans)
then show ?thesis
using ione jone hj Xim invu_nsets unfolding h_def
by (fastforce simp add: image_subset_iff)
qed
moreover have "insert p (u ` V) \<in> nsets {..p} q2"
by (simp add: ione inq1)
ultimately show ?thesis
by (metis ione image_subsetI insertI1 lessI nth_Cons_0 nth_Cons_Suc)
next
case jzero
then have "u ` V \<in> nsets {..p} q1"
using V u_nsets by auto
moreover have "f ` nsets (u ` V) (Suc r) \<subseteq> {j}"
using hj
apply (clarsimp simp add: h_def image_subset_iff nsets_def)
by (metis Zero_not_Suc card_eq_0_iff card_image subset_image_inj)
ultimately show ?thesis
using jzero not_less_eq by fastforce
qed
qed
qed
then show "partn_lst {..<Suc p} [q1,q2] (Suc r)"
using lessThan_Suc lessThan_Suc_atMost by (auto simp: partn_lst_def insert_commute)
qed
qed
qed
qed
qed
subsubsection \<open>Full Ramsey's theorem with multiple colours and arbitrary exponents\<close>
theorem ramsey_full: "\<exists>N::nat. partn_lst {..<N} qs r"
proof (induction k \<equiv> "length qs" arbitrary: qs)
case 0
then show ?case
by (rule_tac x=" r" in exI) (simp add: partn_lst_def)
next
case (Suc k)
note IH = this
show ?case
proof (cases k)
case 0
with Suc obtain q where "qs = [q]"
by (metis length_0_conv length_Suc_conv)
then show ?thesis
by (rule_tac x=q in exI) (auto simp: partn_lst_def funcset_to_empty_iff)
next
case (Suc k')
then obtain q1 q2 l where qs: "qs = q1#q2#l"
by (metis Suc.hyps(2) length_Suc_conv)
then obtain q::nat where q: "partn_lst {..<q} [q1,q2] r"
using ramsey2_full by blast
then obtain p::nat where p: "partn_lst {..<p} (q#l) r"
using IH \<open>qs = q1 # q2 # l\<close> by fastforce
have keq: "Suc (length l) = k"
using IH qs by auto
show ?thesis
proof (intro exI conjI)
show "partn_lst {..<p} qs r"
proof (auto simp: partn_lst_def)
fix f
assume f: "f \<in> nsets {..<p} r \<rightarrow> {..<length qs}"
define g where "g \<equiv> \<lambda>X. if f X < Suc (Suc 0) then 0 else f X - Suc 0"
have "g \<in> nsets {..<p} r \<rightarrow> {..<k}"
unfolding g_def using f Suc IH
by (auto simp: Pi_def not_less)
then obtain i U where i: "i < k" and gi: "g ` nsets U r \<subseteq> {i}"
and U: "U \<in> nsets {..<p} ((q#l) ! i)"
using p keq by (auto simp: partn_lst_def)
show "\<exists>i<length qs. \<exists>H\<in>nsets {..<p} (qs ! i). f ` nsets H r \<subseteq> {i}"
proof (cases "i = 0")
case True
then have "U \<in> nsets {..<p} q" and f01: "f ` nsets U r \<subseteq> {0, Suc 0}"
using U gi unfolding g_def by (auto simp: image_subset_iff)
then obtain u where u: "bij_betw u {..<q} U"
using ex_bij_betw_nat_finite lessThan_atLeast0 by (fastforce simp add: nsets_def)
then have Usub: "U \<subseteq> {..<p}"
by (smt (verit) U mem_Collect_eq nsets_def)
have u_nsets: "u ` X \<in> nsets {..<p} n" if "X \<in> nsets {..<q} n" for X n
proof -
have "inj_on u X"
using u that bij_betw_imp_inj_on inj_on_subset
by (force simp: nsets_def)
then show ?thesis
using Usub u that bij_betwE
by (fastforce simp add: nsets_def card_image)
qed
define h where "h \<equiv> \<lambda>X. f (u ` X)"
have "f (u ` X) < Suc (Suc 0)" if "X \<in> nsets {..<q} r" for X
proof -
have "u ` X \<in> nsets U r"
using u u_nsets that by (auto simp: nsets_def bij_betwE subset_eq)
then show ?thesis
using f01 by auto
qed
then have "h \<in> nsets {..<q} r \<rightarrow> {..<Suc (Suc 0)}"
unfolding h_def by blast
then obtain j V where j: "j < Suc (Suc 0)" and hj: "h ` nsets V r \<subseteq> {j}"
and V: "V \<in> nsets {..<q} ([q1,q2] ! j)"
using q by (auto simp: partn_lst_def)
show ?thesis
proof (intro exI conjI bexI)
show "j < length qs"
using Suc Suc.hyps(2) j by linarith
have "nsets (u ` V) r \<subseteq> (\<lambda>x. (u ` x)) ` nsets V r"
apply (clarsimp simp add: nsets_def image_iff)
by (metis card_eq_0_iff card_image image_is_empty subset_image_inj)
then have "f ` nsets (u ` V) r \<subseteq> h ` nsets V r"
by (auto simp: h_def)
then show "f ` nsets (u ` V) r \<subseteq> {j}"
using hj by auto
show "(u ` V) \<in> nsets {..<p} (qs ! j)"
using V j less_2_cases numeral_2_eq_2 qs u_nsets by fastforce
qed
next
case False
show ?thesis
proof (intro exI conjI bexI)
show "Suc i < length qs"
using Suc.hyps(2) i by auto
show "f ` nsets U r \<subseteq> {Suc i}"
using i gi False
apply (auto simp: g_def image_subset_iff)
by (metis Suc_lessD Suc_pred g_def gi image_subset_iff not_less_eq singleton_iff)
show "U \<in> nsets {..<p} (qs ! (Suc i))"
using False U qs by auto
qed
qed
qed
qed
qed
qed
subsubsection \<open>Simple graph version\<close>
text \<open>This is the most basic version in terms of cliques and independent
sets, i.e. the version for graphs and 2 colours.
\<close>
definition "clique V E \<longleftrightarrow> (\<forall>v\<in>V. \<forall>w\<in>V. v \<noteq> w \<longrightarrow> {v, w} \<in> E)"
definition "indep V E \<longleftrightarrow> (\<forall>v\<in>V. \<forall>w\<in>V. v \<noteq> w \<longrightarrow> {v, w} \<notin> E)"
lemma ramsey2:
"\<exists>r\<ge>1. \<forall>(V::'a set) (E::'a set set). finite V \<and> card V \<ge> r \<longrightarrow>
(\<exists>R \<subseteq> V. card R = m \<and> clique R E \<or> card R = n \<and> indep R E)"
proof -
obtain N where "N \<ge> Suc 0" and N: "partn_lst {..<N} [m,n] 2"
using ramsey2_full nat_le_linear partn_lst_greater_resource by blast
have "\<exists>R\<subseteq>V. card R = m \<and> clique R E \<or> card R = n \<and> indep R E"
if "finite V" "N \<le> card V" for V :: "'a set" and E :: "'a set set"
proof -
from that
obtain v where u: "inj_on v {..<N}" "v ` {..<N} \<subseteq> V"
by (metis card_le_inj card_lessThan finite_lessThan)
define f where "f \<equiv> \<lambda>e. if v ` e \<in> E then 0 else Suc 0"
have f: "f \<in> nsets {..<N} 2 \<rightarrow> {..<Suc (Suc 0)}"
by (simp add: f_def)
then obtain i U where i: "i < 2" and gi: "f ` nsets U 2 \<subseteq> {i}"
and U: "U \<in> nsets {..<N} ([m,n] ! i)"
using N numeral_2_eq_2 by (auto simp: partn_lst_def)
show ?thesis
proof (intro exI conjI)
show "v ` U \<subseteq> V"
using U u by (auto simp: image_subset_iff nsets_def)
show "card (v ` U) = m \<and> clique (v ` U) E \<or> card (v ` U) = n \<and> indep (v ` U) E"
using i unfolding numeral_2_eq_2
using gi U u
apply (simp add: image_subset_iff nsets_2_eq clique_def indep_def less_Suc_eq)
apply (auto simp: f_def nsets_def card_image inj_on_subset split: if_split_asm)
done
qed
qed
then show ?thesis
using \<open>Suc 0 \<le> N\<close> by auto
qed
subsection \<open>Preliminaries\<close>
subsubsection \<open>``Axiom'' of Dependent Choice\<close>
primrec choice :: "('a \<Rightarrow> bool) \<Rightarrow> ('a \<times> 'a) set \<Rightarrow> nat \<Rightarrow> 'a"
where \<comment> \<open>An integer-indexed chain of choices\<close>
choice_0: "choice P r 0 = (SOME x. P x)"
| choice_Suc: "choice P r (Suc n) = (SOME y. P y \<and> (choice P r n, y) \<in> r)"
lemma choice_n:
assumes P0: "P x0"
and Pstep: "\<And>x. P x \<Longrightarrow> \<exists>y. P y \<and> (x, y) \<in> r"
shows "P (choice P r n)"
proof (induct n)
case 0
show ?case by (force intro: someI P0)
next
case Suc
then show ?case by (auto intro: someI2_ex [OF Pstep])
qed
lemma dependent_choice:
assumes trans: "trans r"
and P0: "P x0"
and Pstep: "\<And>x. P x \<Longrightarrow> \<exists>y. P y \<and> (x, y) \<in> r"
obtains f :: "nat \<Rightarrow> 'a" where "\<And>n. P (f n)" and "\<And>n m. n < m \<Longrightarrow> (f n, f m) \<in> r"
proof
fix n
show "P (choice P r n)"
by (blast intro: choice_n [OF P0 Pstep])
next
fix n m :: nat
assume "n < m"
from Pstep [OF choice_n [OF P0 Pstep]] have "(choice P r k, choice P r (Suc k)) \<in> r" for k
by (auto intro: someI2_ex)
then show "(choice P r n, choice P r m) \<in> r"
by (auto intro: less_Suc_induct [OF \<open>n < m\<close>] transD [OF trans])
qed
subsubsection \<open>Partition functions\<close>
definition part_fn :: "nat \<Rightarrow> nat \<Rightarrow> 'a set \<Rightarrow> ('a set \<Rightarrow> nat) \<Rightarrow> bool"
\<comment> \<open>the function \<^term>\<open>f\<close> partitions the \<^term>\<open>r\<close>-subsets of the typically
infinite set \<^term>\<open>Y\<close> into \<^term>\<open>s\<close> distinct categories.\<close>
where "part_fn r s Y f \<longleftrightarrow> (f \<in> nsets Y r \<rightarrow> {..<s})"
text \<open>For induction, we decrease the value of \<^term>\<open>r\<close> in partitions.\<close>
lemma part_fn_Suc_imp_part_fn:
"\<lbrakk>infinite Y; part_fn (Suc r) s Y f; y \<in> Y\<rbrakk> \<Longrightarrow> part_fn r s (Y - {y}) (\<lambda>u. f (insert y u))"
by (simp add: part_fn_def nsets_def Pi_def subset_Diff_insert)
lemma part_fn_subset: "part_fn r s YY f \<Longrightarrow> Y \<subseteq> YY \<Longrightarrow> part_fn r s Y f"
unfolding part_fn_def nsets_def by blast
subsection \<open>Ramsey's Theorem: Infinitary Version\<close>
lemma Ramsey_induction:
fixes s r :: nat
and YY :: "'a set"
and f :: "'a set \<Rightarrow> nat"
assumes "infinite YY" "part_fn r s YY f"
shows "\<exists>Y' t'. Y' \<subseteq> YY \<and> infinite Y' \<and> t' < s \<and> (\<forall>X. X \<subseteq> Y' \<and> finite X \<and> card X = r \<longrightarrow> f X = t')"
using assms
proof (induct r arbitrary: YY f)
case 0
then show ?case
by (auto simp add: part_fn_def card_eq_0_iff cong: conj_cong)
next
case (Suc r)
show ?case
proof -
from Suc.prems infinite_imp_nonempty obtain yy where yy: "yy \<in> YY"
by blast
let ?ramr = "{((y, Y, t), (y', Y', t')). y' \<in> Y \<and> Y' \<subseteq> Y}"
let ?propr = "\<lambda>(y, Y, t).
y \<in> YY \<and> y \<notin> Y \<and> Y \<subseteq> YY \<and> infinite Y \<and> t < s
\<and> (\<forall>X. X\<subseteq>Y \<and> finite X \<and> card X = r \<longrightarrow> (f \<circ> insert y) X = t)"
from Suc.prems have infYY': "infinite (YY - {yy})" by auto
from Suc.prems have partf': "part_fn r s (YY - {yy}) (f \<circ> insert yy)"
by (simp add: o_def part_fn_Suc_imp_part_fn yy)
have transr: "trans ?ramr" by (force simp add: trans_def)
from Suc.hyps [OF infYY' partf']
obtain Y0 and t0 where "Y0 \<subseteq> YY - {yy}" "infinite Y0" "t0 < s"
"X \<subseteq> Y0 \<and> finite X \<and> card X = r \<longrightarrow> (f \<circ> insert yy) X = t0" for X
by blast
with yy have propr0: "?propr(yy, Y0, t0)" by blast
have proprstep: "\<exists>y. ?propr y \<and> (x, y) \<in> ?ramr" if x: "?propr x" for x
proof (cases x)
case (fields yx Yx tx)
with x obtain yx' where yx': "yx' \<in> Yx"
by (blast dest: infinite_imp_nonempty)
from fields x have infYx': "infinite (Yx - {yx'})" by auto
with fields x yx' Suc.prems have partfx': "part_fn r s (Yx - {yx'}) (f \<circ> insert yx')"
by (simp add: o_def part_fn_Suc_imp_part_fn part_fn_subset [where YY=YY and Y=Yx])
from Suc.hyps [OF infYx' partfx'] obtain Y' and t'
where Y': "Y' \<subseteq> Yx - {yx'}" "infinite Y'" "t' < s"
"X \<subseteq> Y' \<and> finite X \<and> card X = r \<longrightarrow> (f \<circ> insert yx') X = t'" for X
by blast
from fields x Y' yx' have "?propr (yx', Y', t') \<and> (x, (yx', Y', t')) \<in> ?ramr"
by blast
then show ?thesis ..
qed
from dependent_choice [OF transr propr0 proprstep]
obtain g where pg: "?propr (g n)" and rg: "n < m \<Longrightarrow> (g n, g m) \<in> ?ramr" for n m :: nat
by blast
let ?gy = "fst \<circ> g"
let ?gt = "snd \<circ> snd \<circ> g"
have rangeg: "\<exists>k. range ?gt \<subseteq> {..<k}"
proof (intro exI subsetI)
fix x
assume "x \<in> range ?gt"
then obtain n where "x = ?gt n" ..
with pg [of n] show "x \<in> {..<s}" by (cases "g n") auto
qed
from rangeg have "finite (range ?gt)"
by (simp add: finite_nat_iff_bounded)
then obtain s' and n' where s': "s' = ?gt n'" and infeqs': "infinite {n. ?gt n = s'}"
by (rule inf_img_fin_domE) (auto simp add: vimage_def intro: infinite_UNIV_nat)
with pg [of n'] have less': "s'<s" by (cases "g n'") auto
have inj_gy: "inj ?gy"
proof (rule linorder_injI)
fix m m' :: nat
assume "m < m'"
from rg [OF this] pg [of m] show "?gy m \<noteq> ?gy m'"
by (cases "g m", cases "g m'") auto
qed
show ?thesis
proof (intro exI conjI)
from pg show "?gy ` {n. ?gt n = s'} \<subseteq> YY"
by (auto simp add: Let_def split_beta)
from infeqs' show "infinite (?gy ` {n. ?gt n = s'})"
by (blast intro: inj_gy [THEN subset_inj_on] dest: finite_imageD)
show "s' < s" by (rule less')
show "\<forall>X. X \<subseteq> ?gy ` {n. ?gt n = s'} \<and> finite X \<and> card X = Suc r \<longrightarrow> f X = s'"
proof -
have "f X = s'"
if X: "X \<subseteq> ?gy ` {n. ?gt n = s'}"
and cardX: "finite X" "card X = Suc r"
for X
proof -
from X obtain AA where AA: "AA \<subseteq> {n. ?gt n = s'}" and Xeq: "X = ?gy`AA"
by (auto simp add: subset_image_iff)
with cardX have "AA \<noteq> {}" by auto
then have AAleast: "(LEAST x. x \<in> AA) \<in> AA" by (auto intro: LeastI_ex)
show ?thesis
proof (cases "g (LEAST x. x \<in> AA)")
case (fields ya Ya ta)
with AAleast Xeq have ya: "ya \<in> X" by (force intro!: rev_image_eqI)
then have "f X = f (insert ya (X - {ya}))" by (simp add: insert_absorb)
also have "\<dots> = ta"
proof -
have *: "X - {ya} \<subseteq> Ya"
proof
fix x assume x: "x \<in> X - {ya}"
then obtain a' where xeq: "x = ?gy a'" and a': "a' \<in> AA"
by (auto simp add: Xeq)
with fields x have "a' \<noteq> (LEAST x. x \<in> AA)" by auto
with Least_le [of "\<lambda>x. x \<in> AA", OF a'] have "(LEAST x. x \<in> AA) < a'"
by arith
from xeq fields rg [OF this] show "x \<in> Ya" by auto
qed
have "card (X - {ya}) = r"
by (simp add: cardX ya)
with pg [of "LEAST x. x \<in> AA"] fields cardX * show ?thesis
by (auto simp del: insert_Diff_single)
qed
also from AA AAleast fields have "\<dots> = s'" by auto
finally show ?thesis .
qed
qed
then show ?thesis by blast
qed
qed
qed
qed
theorem Ramsey:
fixes s r :: nat
and Z :: "'a set"
and f :: "'a set \<Rightarrow> nat"
shows
"\<lbrakk>infinite Z;
\<forall>X. X \<subseteq> Z \<and> finite X \<and> card X = r \<longrightarrow> f X < s\<rbrakk>
\<Longrightarrow> \<exists>Y t. Y \<subseteq> Z \<and> infinite Y \<and> t < s
\<and> (\<forall>X. X \<subseteq> Y \<and> finite X \<and> card X = r \<longrightarrow> f X = t)"
by (blast intro: Ramsey_induction [unfolded part_fn_def nsets_def])
corollary Ramsey2:
fixes s :: nat
and Z :: "'a set"
and f :: "'a set \<Rightarrow> nat"
assumes infZ: "infinite Z"
and part: "\<forall>x\<in>Z. \<forall>y\<in>Z. x \<noteq> y \<longrightarrow> f {x, y} < s"
shows "\<exists>Y t. Y \<subseteq> Z \<and> infinite Y \<and> t < s \<and> (\<forall>x\<in>Y. \<forall>y\<in>Y. x\<noteq>y \<longrightarrow> f {x, y} = t)"
proof -
from part have part2: "\<forall>X. X \<subseteq> Z \<and> finite X \<and> card X = 2 \<longrightarrow> f X < s"
by (fastforce simp add: eval_nat_numeral card_Suc_eq)
obtain Y t where *:
"Y \<subseteq> Z" "infinite Y" "t < s" "(\<forall>X. X \<subseteq> Y \<and> finite X \<and> card X = 2 \<longrightarrow> f X = t)"
by (insert Ramsey [OF infZ part2]) auto
then have "\<forall>x\<in>Y. \<forall>y\<in>Y. x \<noteq> y \<longrightarrow> f {x, y} = t" by auto
with * show ?thesis by iprover
qed
corollary Ramsey_nsets:
fixes f :: "'a set \<Rightarrow> nat"
assumes "infinite Z" "f ` nsets Z r \<subseteq> {..<s}"
obtains Y t where "Y \<subseteq> Z" "infinite Y" "t < s" "f ` nsets Y r \<subseteq> {t}"
using Ramsey [of Z r f s] assms by (auto simp: nsets_def image_subset_iff)
subsection \<open>Disjunctive Well-Foundedness\<close>
text \<open>
An application of Ramsey's theorem to program termination. See
@{cite "Podelski-Rybalchenko"}.
\<close>
definition disj_wf :: "('a \<times> 'a) set \<Rightarrow> bool"
where "disj_wf r \<longleftrightarrow> (\<exists>T. \<exists>n::nat. (\<forall>i<n. wf (T i)) \<and> r = (\<Union>i<n. T i))"
definition transition_idx :: "(nat \<Rightarrow> 'a) \<Rightarrow> (nat \<Rightarrow> ('a \<times> 'a) set) \<Rightarrow> nat set \<Rightarrow> nat"
where "transition_idx s T A = (LEAST k. \<exists>i j. A = {i, j} \<and> i < j \<and> (s j, s i) \<in> T k)"
lemma transition_idx_less:
assumes "i < j" "(s j, s i) \<in> T k" "k < n"
shows "transition_idx s T {i, j} < n"
proof -
from assms(1,2) have "transition_idx s T {i, j} \<le> k"
by (simp add: transition_idx_def, blast intro: Least_le)
with assms(3) show ?thesis by simp
qed
lemma transition_idx_in:
assumes "i < j" "(s j, s i) \<in> T k"
shows "(s j, s i) \<in> T (transition_idx s T {i, j})"
using assms
by (simp add: transition_idx_def doubleton_eq_iff conj_disj_distribR cong: conj_cong) (erule LeastI)
text \<open>To be equal to the union of some well-founded relations is equivalent
to being the subset of such a union.\<close>
lemma disj_wf: "disj_wf r \<longleftrightarrow> (\<exists>T. \<exists>n::nat. (\<forall>i<n. wf(T i)) \<and> r \<subseteq> (\<Union>i<n. T i))"
proof -
have *: "\<And>T n. \<lbrakk>\<forall>i<n. wf (T i); r \<subseteq> \<Union> (T ` {..<n})\<rbrakk>
\<Longrightarrow> (\<forall>i<n. wf (T i \<inter> r)) \<and> r = (\<Union>i<n. T i \<inter> r)"
by (force simp add: wf_Int1)
show ?thesis
unfolding disj_wf_def by auto (metis "*")
qed
theorem trans_disj_wf_implies_wf:
assumes "trans r"
and "disj_wf r"
shows "wf r"
proof (simp only: wf_iff_no_infinite_down_chain, rule notI)
assume "\<exists>s. \<forall>i. (s (Suc i), s i) \<in> r"
then obtain s where sSuc: "\<forall>i. (s (Suc i), s i) \<in> r" ..
from \<open>disj_wf r\<close> obtain T and n :: nat where wfT: "\<forall>k<n. wf(T k)" and r: "r = (\<Union>k<n. T k)"
by (auto simp add: disj_wf_def)
have s_in_T: "\<exists>k. (s j, s i) \<in> T k \<and> k<n" if "i < j" for i j
proof -
from \<open>i < j\<close> have "(s j, s i) \<in> r"
proof (induct rule: less_Suc_induct)
case 1
then show ?case by (simp add: sSuc)
next
case 2
with \<open>trans r\<close> show ?case
unfolding trans_def by blast
qed
then show ?thesis by (auto simp add: r)
qed
have "i < j \<Longrightarrow> transition_idx s T {i, j} < n" for i j
using s_in_T transition_idx_less by blast
then have trless: "i \<noteq> j \<Longrightarrow> transition_idx s T {i, j} < n" for i j
by (metis doubleton_eq_iff less_linear)
have "\<exists>K k. K \<subseteq> UNIV \<and> infinite K \<and> k < n \<and>
(\<forall>i\<in>K. \<forall>j\<in>K. i \<noteq> j \<longrightarrow> transition_idx s T {i, j} = k)"
by (rule Ramsey2) (auto intro: trless infinite_UNIV_nat)
then obtain K and k where infK: "infinite K" and "k < n"
and allk: "\<forall>i\<in>K. \<forall>j\<in>K. i \<noteq> j \<longrightarrow> transition_idx s T {i, j} = k"
by auto
have "(s (enumerate K (Suc m)), s (enumerate K m)) \<in> T k" for m :: nat
proof -
let ?j = "enumerate K (Suc m)"
let ?i = "enumerate K m"
have ij: "?i < ?j" by (simp add: enumerate_step infK)
have "?j \<in> K" "?i \<in> K" by (simp_all add: enumerate_in_set infK)
with ij have k: "k = transition_idx s T {?i, ?j}" by (simp add: allk)
from s_in_T [OF ij] obtain k' where "(s ?j, s ?i) \<in> T k'" "k'<n" by blast
then show "(s ?j, s ?i) \<in> T k" by (simp add: k transition_idx_in ij)
qed
then have "\<not> wf (T k)"
unfolding wf_iff_no_infinite_down_chain by iprover
with wfT \<open>k < n\<close> show False by blast
qed
end