Theory Abstract-Rewriting.Abstract_Rewriting
section ‹Abstract Rewrite Systems›
theory Abstract_Rewriting
imports
"HOL-Library.Infinite_Set"
"Regular-Sets.Regexp_Method"
Seq
begin
lemma trancl_mono_set:
"r ⊆ s ⟹ r⇧+ ⊆ s⇧+"
by (blast intro: trancl_mono)
lemma relpow_mono:
fixes r :: "'a rel"
assumes "r ⊆ r'" shows "r ^^ n ⊆ r' ^^ n"
using assms by (induct n) auto
lemma refl_inv_image:
"refl R ⟹ refl (inv_image R f)"
by (simp add: inv_image_def refl_on_def)
subsection ‹Definitions›
text ‹Two elements are \emph{joinable} (and then have in the joinability relation)
w.r.t.\ @{term "A"}, iff they have a common reduct.›
definition join :: "'a rel ⇒ 'a rel" ("(_⇧↓)" [1000] 999) where
"A⇧↓ = A⇧* O (A¯)⇧*"
text ‹Two elements are \emph{meetable} (and then have in the meetability relation)
w.r.t.\ @{term "A"}, iff they have a common ancestor.›
definition meet :: "'a rel ⇒ 'a rel" ("(_⇧↑)" [1000] 999) where
"A⇧↑ = (A¯)⇧* O A⇧*"
text ‹The \emph{symmetric closure} of a relation allows steps in both directions.›
abbreviation symcl :: "'a rel ⇒ 'a rel" ("(_⇧↔)" [1000] 999) where
"A⇧↔ ≡ A ∪ A¯"
text ‹A \emph{conversion} is a (possibly empty) sequence of steps in the symmetric closure.›
definition conversion :: "'a rel ⇒ 'a rel" ("(_⇧↔⇧*)" [1000] 999) where
"A⇧↔⇧* = (A⇧↔)⇧*"
text ‹The set of \emph{normal forms} of an ARS constitutes all the elements that do
not have any successors.›
definition NF :: "'a rel ⇒ 'a set" where
"NF A = {a. A `` {a} = {}}"
definition normalizability :: "'a rel ⇒ 'a rel" ("(_⇧!)" [1000] 999) where
"A⇧! = {(a, b). (a, b) ∈ A⇧* ∧ b ∈ NF A}"
notation (ASCII)
symcl ("(_^<->)" [1000] 999) and
conversion ("(_^<->*)" [1000] 999) and
normalizability ("(_^!)" [1000] 999)
lemma symcl_converse:
"(A⇧↔)¯ = A⇧↔" by auto
lemma symcl_Un: "(A ∪ B)⇧↔ = A⇧↔ ∪ B⇧↔" by auto
lemma no_step:
assumes "A `` {a} = {}" shows "a ∈ NF A"
using assms by (auto simp: NF_def)
lemma joinI:
"(a, c) ∈ A⇧* ⟹ (b, c) ∈ A⇧* ⟹ (a, b) ∈ A⇧↓"
by (auto simp: join_def rtrancl_converse)
lemma joinI_left:
"(a, b) ∈ A⇧* ⟹ (a, b) ∈ A⇧↓"
by (auto simp: join_def)
lemma joinI_right: "(b, a) ∈ A⇧* ⟹ (a, b) ∈ A⇧↓"
by (rule joinI) auto
lemma joinE:
assumes "(a, b) ∈ A⇧↓"
obtains c where "(a, c) ∈ A⇧*" and "(b, c) ∈ A⇧*"
using assms by (auto simp: join_def rtrancl_converse)
lemma joinD:
"(a, b) ∈ A⇧↓ ⟹ ∃c. (a, c) ∈ A⇧* ∧ (b, c) ∈ A⇧*"
by (blast elim: joinE)
lemma meetI:
"(a, b) ∈ A⇧* ⟹ (a, c) ∈ A⇧* ⟹ (b, c) ∈ A⇧↑"
by (auto simp: meet_def rtrancl_converse)
lemma meetE:
assumes "(b, c) ∈ A⇧↑"
obtains a where "(a, b) ∈ A⇧*" and "(a, c) ∈ A⇧*"
using assms by (auto simp: meet_def rtrancl_converse)
lemma meetD: "(b, c) ∈ A⇧↑ ⟹ ∃a. (a, b) ∈ A⇧* ∧ (a, c) ∈ A⇧*"
by (blast elim: meetE)
lemma conversionI: "(a, b) ∈ (A⇧↔)⇧* ⟹ (a, b) ∈ A⇧↔⇧*"
by (simp add: conversion_def)
lemma conversion_refl [simp]: "(a, a) ∈ A⇧↔⇧*"
by (simp add: conversion_def)
lemma conversionI':
assumes "(a, b) ∈ A⇧*" shows "(a, b) ∈ A⇧↔⇧*"
using assms
proof (induct)
case base then show ?case by simp
next
case (step b c)
then have "(b, c) ∈ A⇧↔" by simp
with ‹(a, b) ∈ A⇧↔⇧*› show ?case unfolding conversion_def by (rule rtrancl.intros)
qed
lemma rtrancl_comp_trancl_conv:
"r⇧* O r = r⇧+" by regexp
lemma trancl_o_refl_is_trancl:
"r⇧+ O r⇧= = r⇧+" by regexp
lemma conversionE:
"(a, b) ∈ A⇧↔⇧* ⟹ ((a, b) ∈ (A⇧↔)⇧* ⟹ P) ⟹ P"
by (simp add: conversion_def)
text ‹Later declarations are tried first for `proof' and `rule,' then have the ``main''
introduction\,/\, elimination rules for constants should be declared last.›
declare joinI_left [intro]
declare joinI_right [intro]
declare joinI [intro]
declare joinD [dest]
declare joinE [elim]
declare meetI [intro]
declare meetD [dest]
declare meetE [elim]
declare conversionI' [intro]
declare conversionI [intro]
declare conversionE [elim]
lemma conversion_trans:
"trans (A⇧↔⇧*)"
unfolding trans_def
proof (intro allI impI)
fix a b c assume "(a, b) ∈ A⇧↔⇧*" and "(b, c) ∈ A⇧↔⇧*"
then show "(a, c) ∈ A⇧↔⇧*" unfolding conversion_def
proof (induct)
case base then show ?case by simp
next
case (step b c')
from ‹(b, c') ∈ A⇧↔› and ‹(c', c) ∈ (A⇧↔)⇧*›
have "(b, c) ∈ (A⇧↔)⇧*" by (rule converse_rtrancl_into_rtrancl)
with step show ?case by simp
qed
qed
lemma conversion_sym:
"sym (A⇧↔⇧*)"
unfolding sym_def
proof (intro allI impI)
fix a b assume "(a, b) ∈ A⇧↔⇧*" then show "(b, a) ∈ A⇧↔⇧*" unfolding conversion_def
proof (induct)
case base then show ?case by simp
next
case (step b c)
then have "(c, b) ∈ A⇧↔" by blast
from ‹(c, b) ∈ A⇧↔› and ‹(b, a) ∈ (A⇧↔)⇧*›
show ?case by (rule converse_rtrancl_into_rtrancl)
qed
qed
lemma conversion_inv:
"(x, y) ∈ R⇧↔⇧* ⟷ (y, x) ∈ R⇧↔⇧*"
by (auto simp: conversion_def)
(metis (full_types) rtrancl_converseD symcl_converse)+
lemma conversion_converse [simp]:
"(A⇧↔⇧*)¯ = A⇧↔⇧*"
by (metis conversion_sym sym_conv_converse_eq)
lemma conversion_rtrancl [simp]:
"(A⇧↔⇧*)⇧* = A⇧↔⇧*"
by (metis conversion_def rtrancl_idemp)
lemma rtrancl_join_join:
assumes "(a, b) ∈ A⇧*" and "(b, c) ∈ A⇧↓" shows "(a, c) ∈ A⇧↓"
proof -
from ‹(b, c) ∈ A⇧↓› obtain b' where "(b, b') ∈ A⇧*" and "(b', c) ∈ (A¯)⇧*"
unfolding join_def by blast
with ‹(a, b) ∈ A⇧*› have "(a, b') ∈ A⇧*" by simp
with ‹(b', c) ∈ (A¯)⇧*› show ?thesis unfolding join_def by blast
qed
lemma join_rtrancl_join:
assumes "(a, b) ∈ A⇧↓" and "(c, b) ∈ A⇧*" shows "(a, c) ∈ A⇧↓"
proof -
from ‹(c, b) ∈ A⇧*› have "(b, c) ∈ (A¯)⇧*" unfolding rtrancl_converse by simp
from ‹(a, b) ∈ A⇧↓› obtain a' where "(a, a') ∈ A⇧*" and "(a', b) ∈ (A¯)⇧*"
unfolding join_def by best
with ‹(b, c) ∈ (A¯)⇧*› have "(a', c) ∈ (A¯)⇧*" by simp
with ‹(a, a') ∈ A⇧*› show ?thesis unfolding join_def by blast
qed
lemma NF_I: "(⋀b. (a, b) ∉ A) ⟹ a ∈ NF A" by (auto intro: no_step)
lemma NF_E: "a ∈ NF A ⟹ ((a, b) ∉ A ⟹ P) ⟹ P" by (auto simp: NF_def)
declare NF_I [intro]
declare NF_E [elim]
lemma NF_no_step: "a ∈ NF A ⟹ ∀b. (a, b) ∉ A" by auto
lemma NF_anti_mono:
assumes "A ⊆ B" shows "NF B ⊆ NF A"
using assms by auto
lemma NF_iff_no_step: "a ∈ NF A = (∀b. (a, b) ∉ A)" by auto
lemma NF_no_trancl_step:
assumes "a ∈ NF A" shows "∀b. (a, b) ∉ A⇧+"
proof -
from assms have "∀b. (a, b) ∉ A" by auto
show ?thesis
proof (intro allI notI)
fix b assume "(a, b) ∈ A⇧+"
then show False by (induct) (auto simp: ‹∀b. (a, b) ∉ A›)
qed
qed
lemma NF_Id_on_fst_image [simp]: "NF (Id_on (fst ` A)) = NF A" by force
lemma fst_image_NF_Id_on [simp]: "fst ` R = Q ⟹ NF (Id_on Q) = NF R" by force
lemma NF_empty [simp]: "NF {} = UNIV" by auto
lemma normalizability_I: "(a, b) ∈ A⇧* ⟹ b ∈ NF A ⟹ (a, b) ∈ A⇧!"
by (simp add: normalizability_def)
lemma normalizability_I': "(a, b) ∈ A⇧* ⟹ (b, c) ∈ A⇧! ⟹ (a, c) ∈ A⇧!"
by (auto simp add: normalizability_def)
lemma normalizability_E: "(a, b) ∈ A⇧! ⟹ ((a, b) ∈ A⇧* ⟹ b ∈ NF A ⟹ P) ⟹ P"
by (simp add: normalizability_def)
declare normalizability_I' [intro]
declare normalizability_I [intro]
declare normalizability_E [elim]
subsection ‹Properties of ARSs›
text ‹The following properties on (elements of) ARSs are defined: completeness,
Church-Rosser property, semi-completeness, strong normalization, unique normal
forms, Weak Church-Rosser property, and weak normalization.›
definition CR_on :: "'a rel ⇒ 'a set ⇒ bool" where
"CR_on r A ⟷ (∀a∈A. ∀b c. (a, b) ∈ r⇧* ∧ (a, c) ∈ r⇧* ⟶ (b, c) ∈ join r)"
abbreviation CR :: "'a rel ⇒ bool" where
"CR r ≡ CR_on r UNIV"
definition SN_on :: "'a rel ⇒ 'a set ⇒ bool" where
"SN_on r A ⟷ ¬ (∃f. f 0 ∈ A ∧ chain r f)"
abbreviation SN :: "'a rel ⇒ bool" where
"SN r ≡ SN_on r UNIV"
text ‹Alternative definition of @{term "SN"}.›
lemma SN_def: "SN r = (∀x. SN_on r {x})"
unfolding SN_on_def by blast
definition UNF_on :: "'a rel ⇒ 'a set ⇒ bool" where
"UNF_on r A ⟷ (∀a∈A. ∀b c. (a, b) ∈ r⇧! ∧ (a, c) ∈ r⇧! ⟶ b = c)"
abbreviation UNF :: "'a rel ⇒ bool" where "UNF r ≡ UNF_on r UNIV"
definition WCR_on :: "'a rel ⇒ 'a set ⇒ bool" where
"WCR_on r A ⟷ (∀a∈A. ∀b c. (a, b) ∈ r ∧ (a, c) ∈ r ⟶ (b, c) ∈ join r)"
abbreviation WCR :: "'a rel ⇒ bool" where "WCR r ≡ WCR_on r UNIV"
definition WN_on :: "'a rel ⇒ 'a set ⇒ bool" where
"WN_on r A ⟷ (∀a∈A. ∃b. (a, b) ∈ r⇧!)"
abbreviation WN :: "'a rel ⇒ bool" where
"WN r ≡ WN_on r UNIV"
lemmas CR_defs = CR_on_def
lemmas SN_defs = SN_on_def
lemmas UNF_defs = UNF_on_def
lemmas WCR_defs = WCR_on_def
lemmas WN_defs = WN_on_def
definition complete_on :: "'a rel ⇒ 'a set ⇒ bool" where
"complete_on r A ⟷ SN_on r A ∧ CR_on r A"
abbreviation complete :: "'a rel ⇒ bool" where
"complete r ≡ complete_on r UNIV"
definition semi_complete_on :: "'a rel ⇒ 'a set ⇒ bool" where
"semi_complete_on r A ⟷ WN_on r A ∧ CR_on r A"
abbreviation semi_complete :: "'a rel ⇒ bool" where
"semi_complete r ≡ semi_complete_on r UNIV"
lemmas complete_defs = complete_on_def
lemmas semi_complete_defs = semi_complete_on_def
text ‹Unique normal forms with respect to conversion.›
definition UNC :: "'a rel ⇒ bool" where
"UNC A ⟷ (∀a b. a ∈ NF A ∧ b ∈ NF A ∧ (a, b) ∈ A⇧↔⇧* ⟶ a = b)"
lemma complete_onI:
"SN_on r A ⟹ CR_on r A ⟹ complete_on r A"
by (simp add: complete_defs)
lemma complete_onE:
"complete_on r A ⟹ (SN_on r A ⟹ CR_on r A ⟹ P) ⟹ P"
by (simp add: complete_defs)
lemma CR_onI:
"(⋀a b c. a ∈ A ⟹ (a, b) ∈ r⇧* ⟹ (a, c) ∈ r⇧* ⟹ (b, c) ∈ join r) ⟹ CR_on r A"
by (simp add: CR_defs)
lemma CR_on_singletonI:
"(⋀b c. (a, b) ∈ r⇧* ⟹ (a, c) ∈ r⇧* ⟹ (b, c) ∈ join r) ⟹ CR_on r {a}"
by (simp add: CR_defs)
lemma CR_onE:
"CR_on r A ⟹ a ∈ A ⟹ ((b, c) ∈ join r ⟹ P) ⟹ ((a, b) ∉ r⇧* ⟹ P) ⟹ ((a, c) ∉ r⇧* ⟹ P) ⟹ P"
unfolding CR_defs by blast
lemma CR_onD:
"CR_on r A ⟹ a ∈ A ⟹ (a, b) ∈ r⇧* ⟹ (a, c) ∈ r⇧* ⟹ (b, c) ∈ join r"
by (blast elim: CR_onE)
lemma semi_complete_onI: "WN_on r A ⟹ CR_on r A ⟹ semi_complete_on r A"
by (simp add: semi_complete_defs)
lemma semi_complete_onE:
"semi_complete_on r A ⟹ (WN_on r A ⟹ CR_on r A ⟹ P) ⟹ P"
by (simp add: semi_complete_defs)
declare semi_complete_onI [intro]
declare semi_complete_onE [elim]
declare complete_onI [intro]
declare complete_onE [elim]
declare CR_onI [intro]
declare CR_on_singletonI [intro]
declare CR_onD [dest]
declare CR_onE [elim]
lemma UNC_I:
"(⋀a b. a ∈ NF A ⟹ b ∈ NF A ⟹ (a, b) ∈ A⇧↔⇧* ⟹ a = b) ⟹ UNC A"
by (simp add: UNC_def)
lemma UNC_E:
"⟦UNC A; a = b ⟹ P; a ∉ NF A ⟹ P; b ∉ NF A ⟹ P; (a, b) ∉ A⇧↔⇧* ⟹ P⟧ ⟹ P"
unfolding UNC_def by blast
lemma UNF_onI: "(⋀a b c. a ∈ A ⟹ (a, b) ∈ r⇧! ⟹ (a, c) ∈ r⇧! ⟹ b = c) ⟹ UNF_on r A"
by (simp add: UNF_defs)
lemma UNF_onE:
"UNF_on r A ⟹ a ∈ A ⟹ (b = c ⟹ P) ⟹ ((a, b) ∉ r⇧! ⟹ P) ⟹ ((a, c) ∉ r⇧! ⟹ P) ⟹ P"
unfolding UNF_on_def by blast
lemma UNF_onD:
"UNF_on r A ⟹ a ∈ A ⟹ (a, b) ∈ r⇧! ⟹ (a, c) ∈ r⇧! ⟹ b = c"
by (blast elim: UNF_onE)
declare UNF_onI [intro]
declare UNF_onD [dest]
declare UNF_onE [elim]
lemma SN_onI:
assumes "⋀f. ⟦f 0 ∈ A; chain r f⟧ ⟹ False"
shows "SN_on r A"
using assms unfolding SN_defs by blast
lemma SN_I: "(⋀a. SN_on A {a}) ⟹ SN A"
unfolding SN_on_def by blast
lemma SN_on_trancl_imp_SN_on:
assumes "SN_on (R⇧+) T" shows "SN_on R T"
proof (rule ccontr)
assume "¬ SN_on R T"
then obtain s where "s 0 ∈ T" and "chain R s" unfolding SN_defs by auto
then have "chain (R⇧+) s" by auto
with ‹s 0 ∈ T› have "¬ SN_on (R⇧+) T" unfolding SN_defs by auto
with assms show False by simp
qed
lemma SN_onE:
assumes "SN_on r A"
and "¬ (∃f. f 0 ∈ A ∧ chain r f) ⟹ P"
shows "P"
using assms unfolding SN_defs by simp
lemma not_SN_onE:
assumes "¬ SN_on r A"
and "⋀f. ⟦f 0 ∈ A; chain r f⟧ ⟹ P"
shows "P"
using assms unfolding SN_defs by blast
declare SN_onI [intro]
declare SN_onE [elim]
declare not_SN_onE [Pure.elim, elim]
lemma refl_not_SN: "(x, x) ∈ R ⟹ ¬ SN R"
unfolding SN_defs by force
lemma SN_on_irrefl:
assumes "SN_on r A"
shows "∀a∈A. (a, a) ∉ r"
proof (intro ballI notI)
fix a assume "a ∈ A" and "(a, a) ∈ r"
with assms show False unfolding SN_defs by auto
qed
lemma WCR_onI: "(⋀a b c. a ∈ A ⟹ (a, b) ∈ r ⟹ (a, c) ∈ r ⟹ (b, c) ∈ join r) ⟹ WCR_on r A"
by (simp add: WCR_defs)
lemma WCR_onE:
"WCR_on r A ⟹ a ∈ A ⟹ ((b, c) ∈ join r ⟹ P) ⟹ ((a, b) ∉ r ⟹ P) ⟹ ((a, c) ∉ r ⟹ P) ⟹ P"
unfolding WCR_on_def by blast
lemma SN_nat_bounded: "SN {(x, y :: nat). x < y ∧ y ≤ b}" (is "SN ?R")
proof
fix f
assume "chain ?R f"
then have steps: "⋀i. (f i, f (Suc i)) ∈ ?R" ..
{
fix i
have inc: "f 0 + i ≤ f i"
proof (induct i)
case 0 then show ?case by auto
next
case (Suc i)
have "f 0 + Suc i ≤ f i + Suc 0" using Suc by simp
also have "... ≤ f (Suc i)" using steps [of i]
by auto
finally show ?case by simp
qed
}
from this [of "Suc b"] steps [of b]
show False by simp
qed
lemma WCR_onD:
"WCR_on r A ⟹ a ∈ A ⟹ (a, b) ∈ r ⟹ (a, c) ∈ r ⟹ (b, c) ∈ join r"
by (blast elim: WCR_onE)
lemma WN_onI: "(⋀a. a ∈ A ⟹ ∃b. (a, b) ∈ r⇧!) ⟹ WN_on r A"
by (auto simp: WN_defs)
lemma WN_onE: "WN_on r A ⟹ a ∈ A ⟹ (⋀b. (a, b) ∈ r⇧! ⟹ P) ⟹ P"
unfolding WN_defs by blast
lemma WN_onD: "WN_on r A ⟹ a ∈ A ⟹ ∃b. (a, b) ∈ r⇧!"
by (blast elim: WN_onE)
declare WCR_onI [intro]
declare WCR_onD [dest]
declare WCR_onE [elim]
declare WN_onI [intro]
declare WN_onD [dest]
declare WN_onE [elim]
text ‹Restricting a relation @{term r} to those elements that are strongly
normalizing with respect to a relation @{term s}.›
definition restrict_SN :: "'a rel ⇒ 'a rel ⇒ 'a rel" where
"restrict_SN r s = {(a, b) | a b. (a, b) ∈ r ∧ SN_on s {a}}"
lemma SN_restrict_SN_idemp [simp]: "SN (restrict_SN A A)"
by (auto simp: restrict_SN_def SN_defs)
lemma SN_on_Image:
assumes "SN_on r A"
shows "SN_on r (r `` A)"
proof
fix f
assume "f 0 ∈ r `` A" and chain: "chain r f"
then obtain a where "a ∈ A" and 1: "(a, f 0) ∈ r" by auto
let ?g = "case_nat a f"
from cons_chain [OF 1 chain] have "chain r ?g" .
moreover have "?g 0 ∈ A" by (simp add: ‹a ∈ A›)
ultimately have "¬ SN_on r A" unfolding SN_defs by best
with assms show False by simp
qed
lemma SN_on_subset2:
assumes "A ⊆ B" and "SN_on r B"
shows "SN_on r A"
using assms unfolding SN_on_def by blast
lemma step_preserves_SN_on:
assumes 1: "(a, b) ∈ r"
and 2: "SN_on r {a}"
shows "SN_on r {b}"
using 1 and SN_on_Image [OF 2] and SN_on_subset2 [of "{b}" "r `` {a}"] by auto
lemma steps_preserve_SN_on: "(a, b) ∈ A⇧* ⟹ SN_on A {a} ⟹ SN_on A {b}"
by (induct rule: rtrancl.induct) (auto simp: step_preserves_SN_on)
lemma relpow_seq:
assumes "(x, y) ∈ r^^n"
shows "∃f. f 0 = x ∧ f n = y ∧ (∀i<n. (f i, f (Suc i)) ∈ r)"
using assms
proof (induct n arbitrary: y)
case 0 then show ?case by auto
next
case (Suc n)
then obtain z where "(x, z) ∈ r^^n" and "(z, y) ∈ r" by auto
from Suc(1)[OF ‹(x, z) ∈ r^^n›]
obtain f where "f 0 = x" and "f n = z" and seq: "∀i<n. (f i, f (Suc i)) ∈ r" by auto
let ?n = "Suc n"
let ?f = "λi. if i = ?n then y else f i"
have "?f ?n = y" by simp
from ‹f 0 = x› have "?f 0 = x" by simp
from seq have seq': "∀i<n. (?f i, ?f (Suc i)) ∈ r" by auto
with ‹f n = z› and ‹(z, y) ∈ r› have "∀i<?n. (?f i, ?f (Suc i)) ∈ r" by auto
with ‹?f 0 = x› and ‹?f ?n = y› show ?case by best
qed
lemma rtrancl_imp_seq:
assumes "(x, y) ∈ r⇧*"
shows "∃f n. f 0 = x ∧ f n = y ∧ (∀i<n. (f i, f (Suc i)) ∈ r)"
using assms [unfolded rtrancl_power] and relpow_seq [of x y _ r] by blast
lemma SN_on_Image_rtrancl:
assumes "SN_on r A"
shows "SN_on r (r⇧* `` A)"
proof
fix f
assume f0: "f 0 ∈ r⇧* `` A" and chain: "chain r f"
then obtain a where a: "a ∈ A" and "(a, f 0) ∈ r⇧*" by auto
then obtain n where "(a, f 0) ∈ r^^n" unfolding rtrancl_power by auto
show False
proof (cases n)
case 0
with ‹(a, f 0) ∈ r^^n› have "f 0 = a" by simp
then have "f 0 ∈ A" by (simp add: a)
with chain have "¬ SN_on r A" by auto
with assms show False by simp
next
case (Suc m)
from relpow_seq [OF ‹(a, f 0) ∈ r^^n›]
obtain g where g0: "g 0 = a" and "g n = f 0"
and gseq: "∀i<n. (g i, g (Suc i)) ∈ r" by auto
let ?f = "λi. if i < n then g i else f (i - n)"
have "chain r ?f"
proof
fix i
{
assume "Suc i < n"
then have "(?f i, ?f (Suc i)) ∈ r" by (simp add: gseq)
}
moreover
{
assume "Suc i > n"
then have eq: "Suc (i - n) = Suc i - n" by arith
from chain have "(f (i - n), f (Suc (i - n))) ∈ r" by simp
then have "(f (i - n), f (Suc i - n)) ∈ r" by (simp add: eq)
with ‹Suc i > n› have "(?f i, ?f (Suc i)) ∈ r" by simp
}
moreover
{
assume "Suc i = n"
then have eq: "f (Suc i - n) = g n" by (simp add: ‹g n = f 0›)
from ‹Suc i = n› have eq': "i = n - 1" by arith
from gseq have "(g i, f (Suc i - n)) ∈ r" unfolding eq by (simp add: Suc eq')
then have "(?f i, ?f (Suc i)) ∈ r" using ‹Suc i = n› by simp
}
ultimately show "(?f i, ?f (Suc i)) ∈ r" by simp
qed
moreover have "?f 0 ∈ A"
proof (cases n)
case 0
with ‹(a, f 0) ∈ r^^n› have eq: "a = f 0" by simp
from a show ?thesis by (simp add: eq 0)
next
case (Suc m)
then show ?thesis by (simp add: a g0)
qed
ultimately have "¬ SN_on r A" unfolding SN_defs by best
with assms show False by simp
qed
qed
declare subrelI [Pure.intro]
lemma restrict_SN_trancl_simp [simp]: "(restrict_SN A A)⇧+ = restrict_SN (A⇧+) A" (is "?lhs = ?rhs")
proof
show "?lhs ⊆ ?rhs"
proof
fix a b assume "(a, b) ∈ ?lhs" then show "(a, b) ∈ ?rhs"
unfolding restrict_SN_def by (induct rule: trancl.induct) auto
qed
next
show "?rhs ⊆ ?lhs"
proof
fix a b assume "(a, b) ∈ ?rhs"
then have "(a, b) ∈ A⇧+" and "SN_on A {a}" unfolding restrict_SN_def by auto
then show "(a, b) ∈ ?lhs"
proof (induct rule: trancl.induct)
case (r_into_trancl x y) then show ?case unfolding restrict_SN_def by auto
next
case (trancl_into_trancl a b c)
then have IH: "(a, b) ∈ ?lhs" by auto
from trancl_into_trancl have "(a, b) ∈ A⇧*" by auto
from this and ‹SN_on A {a}› have "SN_on A {b}" by (rule steps_preserve_SN_on)
with ‹(b, c) ∈ A› have "(b, c) ∈ ?lhs" unfolding restrict_SN_def by auto
with IH show ?case by simp
qed
qed
qed
lemma SN_imp_WN:
assumes "SN A" shows "WN A"
proof -
from ‹SN A› have "wf (A¯)" by (simp add: SN_defs wf_iff_no_infinite_down_chain)
show "WN A"
proof
fix a
show "∃b. (a, b) ∈ A⇧!" unfolding normalizability_def NF_def Image_def
by (rule wfE_min [OF ‹wf (A¯)›, of a "A⇧* `` {a}", simplified])
(auto intro: rtrancl_into_rtrancl)
qed
qed
lemma UNC_imp_UNF:
assumes "UNC r" shows "UNF r"
proof - {
fix x y z assume "(x, y) ∈ r⇧!" and "(x, z) ∈ r⇧!"
then have "(x, y) ∈ r⇧*" and "(x, z) ∈ r⇧*" and "y ∈ NF r" and "z ∈ NF r" by auto
then have "(x, y) ∈ r⇧↔⇧*" and "(x, z) ∈ r⇧↔⇧*" by auto
then have "(z, x) ∈ r⇧↔⇧*" using conversion_sym unfolding sym_def by best
with ‹(x, y) ∈ r⇧↔⇧*› have "(z, y) ∈ r⇧↔⇧*" using conversion_trans unfolding trans_def by best
from assms and this and ‹z ∈ NF r› and ‹y ∈ NF r› have "z = y" unfolding UNC_def by auto
} then show ?thesis by auto
qed
lemma join_NF_imp_eq:
assumes "(x, y) ∈ r⇧↓" and "x ∈ NF r" and "y ∈ NF r"
shows "x = y"
proof -
from ‹(x, y) ∈ r⇧↓› obtain z where "(x, z)∈r⇧*" and "(z, y)∈(r¯)⇧*" unfolding join_def by auto
then have "(y, z) ∈ r⇧*" unfolding rtrancl_converse by simp
from ‹x ∈ NF r› have "(x, z) ∉ r⇧+" using NF_no_trancl_step by best
then have "x = z" using rtranclD [OF ‹(x, z) ∈ r⇧*›] by auto
from ‹y ∈ NF r› have "(y, z) ∉ r⇧+" using NF_no_trancl_step by best
then have "y = z" using rtranclD [OF ‹(y, z) ∈ r⇧*›] by auto
with ‹x = z› show ?thesis by simp
qed
lemma rtrancl_Restr:
assumes "(x, y) ∈ (Restr r A)⇧*"
shows "(x, y) ∈ r⇧*"
using assms by induct auto
lemma join_mono:
assumes "r ⊆ s"
shows "r⇧↓ ⊆ s⇧↓"
using rtrancl_mono [OF assms] by (auto simp: join_def rtrancl_converse)
lemma CR_iff_meet_subset_join: "CR r = (r⇧↑ ⊆ r⇧↓)"
proof
assume "CR r" show "r⇧↑ ⊆ r⇧↓"
proof (rule subrelI)
fix x y assume "(x, y) ∈ r⇧↑"
then obtain z where "(z, x) ∈ r⇧*" and "(z, y) ∈ r⇧*" using meetD by best
with ‹CR r› show "(x, y) ∈ r⇧↓" by (auto simp: CR_defs)
qed
next
assume "r⇧↑ ⊆ r⇧↓" {
fix x y z assume "(x, y) ∈ r⇧*" and "(x, z) ∈ r⇧*"
then have "(y, z) ∈ r⇧↑" unfolding meet_def rtrancl_converse by auto
with ‹r⇧↑ ⊆ r⇧↓› have "(y, z) ∈ r⇧↓" by auto
} then show "CR r" by (auto simp: CR_defs)
qed
lemma CR_divergence_imp_join:
assumes "CR r" and "(x, y) ∈ r⇧*" and "(x, z) ∈ r⇧*"
shows "(y, z) ∈ r⇧↓"
using assms by auto
lemma join_imp_conversion: "r⇧↓ ⊆ r⇧↔⇧*"
proof
fix x z assume "(x, z) ∈ r⇧↓"
then obtain y where "(x, y) ∈ r⇧*" and "(z, y) ∈ r⇧*" by auto
then have "(x, y) ∈ r⇧↔⇧*" and "(z, y) ∈ r⇧↔⇧*" by auto
from ‹(z, y) ∈ r⇧↔⇧*› have "(y, z) ∈ r⇧↔⇧*" using conversion_sym unfolding sym_def by best
with ‹(x, y) ∈ r⇧↔⇧*› show "(x, z) ∈ r⇧↔⇧*" using conversion_trans unfolding trans_def by best
qed
lemma meet_imp_conversion: "r⇧↑ ⊆ r⇧↔⇧*"
proof (rule subrelI)
fix y z assume "(y, z) ∈ r⇧↑"
then obtain x where "(x, y) ∈ r⇧*" and "(x, z) ∈ r⇧*" by auto
then have "(x, y) ∈ r⇧↔⇧*" and "(x, z) ∈ r⇧↔⇧*" by auto
from ‹(x, y) ∈ r⇧↔⇧*› have "(y, x) ∈ r⇧↔⇧*" using conversion_sym unfolding sym_def by best
with ‹(x, z) ∈ r⇧↔⇧*› show "(y, z) ∈ r⇧↔⇧*" using conversion_trans unfolding trans_def by best
qed
lemma CR_imp_UNF:
assumes "CR r" shows "UNF r"
proof - {
fix x y z assume "(x, y) ∈ r⇧!" and "(x, z) ∈ r⇧!"
then have "(x, y) ∈ r⇧*" and "y ∈ NF r" and "(x, z) ∈ r⇧*" and "z ∈ NF r"
unfolding normalizability_def by auto
from assms and ‹(x, y) ∈ r⇧*› and ‹(x, z) ∈ r⇧*› have "(y, z) ∈ r⇧↓"
by (rule CR_divergence_imp_join)
from this and ‹y ∈ NF r› and ‹z ∈ NF r› have "y = z" by (rule join_NF_imp_eq)
} then show ?thesis by auto
qed
lemma CR_iff_conversion_imp_join: "CR r = (r⇧↔⇧* ⊆ r⇧↓)"
proof (intro iffI subrelI)
fix x y assume "CR r" and "(x, y) ∈ r⇧↔⇧*"
then obtain n where "(x, y) ∈ (r⇧↔)^^n" unfolding conversion_def rtrancl_is_UN_relpow by auto
then show "(x, y) ∈ r⇧↓"
proof (induct n arbitrary: x)
case 0
assume "(x, y) ∈ r⇧↔ ^^ 0" then have "x = y" by simp
show ?case unfolding ‹x = y› by auto
next
case (Suc n)
from ‹(x, y) ∈ r⇧↔ ^^ Suc n› obtain z where "(x, z) ∈ r⇧↔" and "(z, y) ∈ r⇧↔ ^^ n"
using relpow_Suc_D2 by best
with Suc have "(z, y) ∈ r⇧↓" by simp
from ‹(x, z) ∈ r⇧↔› show ?case
proof
assume "(x, z) ∈ r" with ‹(z, y) ∈ r⇧↓› show ?thesis by (auto intro: rtrancl_join_join)
next
assume "(x, z) ∈ r¯"
then have "(z, x) ∈ r⇧*" by simp
from ‹(z, y) ∈ r⇧↓› obtain z' where "(z, z') ∈ r⇧*" and "(y, z') ∈ r⇧*" by auto
from ‹CR r› and ‹(z, x) ∈ r⇧*› and ‹(z, z') ∈ r⇧*› have "(x, z') ∈ r⇧↓"
by (rule CR_divergence_imp_join)
then obtain x' where "(x, x') ∈ r⇧*" and "(z', x') ∈ r⇧*" by auto
with ‹(y, z') ∈ r⇧*› show ?thesis by auto
qed
qed
next
assume "r⇧↔⇧* ⊆ r⇧↓" then show "CR r" unfolding CR_iff_meet_subset_join
using meet_imp_conversion by auto
qed
lemma CR_imp_conversionIff_join:
assumes "CR r" shows "r⇧↔⇧* = r⇧↓"
proof
show "r⇧↔⇧* ⊆ r⇧↓" using CR_iff_conversion_imp_join assms by auto
next
show "r⇧↓ ⊆ r⇧↔⇧*" by (rule join_imp_conversion)
qed
lemma sym_join: "sym (join r)" by (auto simp: sym_def)
lemma join_sym: "(s, t) ∈ A⇧↓ ⟹ (t, s) ∈ A⇧↓" by auto
lemma CR_join_left_I:
assumes "CR r" and "(x, y) ∈ r⇧*" and "(x, z) ∈ r⇧↓" shows "(y, z) ∈ r⇧↓"
proof -
from ‹(x, z) ∈ r⇧↓› obtain x' where "(x, x') ∈ r⇧*" and "(z, x') ∈ r⇧↓" by auto
from ‹CR r› and ‹(x, x') ∈ r⇧*› and ‹(x, y) ∈ r⇧*› have "(x, y) ∈ r⇧↓" by auto
then have "(y, x) ∈ r⇧↓" using join_sym by best
from ‹CR r› have "r⇧↔⇧* = r⇧↓" by (rule CR_imp_conversionIff_join)
from ‹(y, x) ∈ r⇧↓› and ‹(x, z) ∈ r⇧↓› show ?thesis using conversion_trans
unfolding trans_def ‹r⇧↔⇧* = r⇧↓› [symmetric] by best
qed
lemma CR_join_right_I:
assumes "CR r" and "(x, y) ∈ r⇧↓" and "(y, z) ∈ r⇧*" shows "(x, z) ∈ r⇧↓"
proof -
have "r⇧↔⇧* = r⇧↓" by (rule CR_imp_conversionIff_join [OF ‹CR r›])
from ‹(y, z) ∈ r⇧*› have "(y, z) ∈ r⇧↔⇧*" by auto
with ‹(x, y) ∈ r⇧↓› show ?thesis unfolding ‹r⇧↔⇧* = r⇧↓› [symmetric] using conversion_trans
unfolding trans_def by fast
qed
lemma NF_not_suc:
assumes "(x, y) ∈ r⇧*" and "x ∈ NF r" shows "x = y"
proof -
from ‹x ∈ NF r› have "∀y. (x, y) ∉ r" using NF_no_step by auto
then have "x ∉ Domain r" unfolding Domain_unfold by simp
from ‹(x, y) ∈ r⇧*› show ?thesis unfolding Not_Domain_rtrancl [OF ‹x ∉ Domain r›] by simp
qed
lemma semi_complete_imp_conversionIff_same_NF:
assumes "semi_complete r"
shows "((x, y) ∈ r⇧↔⇧*) = (∀u v. (x, u) ∈ r⇧! ∧ (y, v) ∈ r⇧! ⟶ u = v)"
proof -
from assms have "WN r" and "CR r" unfolding semi_complete_defs by auto
then have "r⇧↔⇧* = r⇧↓" using CR_imp_conversionIff_join by auto
show ?thesis
proof
assume "(x, y) ∈ r⇧↔⇧*"
from ‹(x, y) ∈ r⇧↔⇧*› have "(x, y) ∈ r⇧↓" unfolding ‹r⇧↔⇧* = r⇧↓› .
show "∀u v. (x, u) ∈ r⇧! ∧ (y, v) ∈ r⇧! ⟶ u = v"
proof (intro allI impI, elim conjE)
fix u v assume "(x, u) ∈ r⇧!" and "(y, v) ∈ r⇧!"
then have "(x, u) ∈ r⇧*" and "(y, v) ∈ r⇧*" and "u ∈ NF r" and "v ∈ NF r" by auto
from ‹CR r› and ‹(x, u) ∈ r⇧*› and ‹(x, y) ∈ r⇧↓› have "(u, y) ∈ r⇧↓"
by (auto intro: CR_join_left_I)
then have "(y, u) ∈ r⇧↓" using join_sym by best
with ‹(x, y) ∈ r⇧↓› have "(x, u) ∈ r⇧↓" unfolding ‹r⇧↔⇧* = r⇧↓› [symmetric]
using conversion_trans unfolding trans_def by best
from ‹CR r› and ‹(x, y) ∈ r⇧↓› and ‹(y, v) ∈ r⇧*› have "(x, v) ∈ r⇧↓"
by (auto intro: CR_join_right_I)
then have "(v, x) ∈ r⇧↓" using join_sym unfolding sym_def by best
with ‹(x, u) ∈ r⇧↓› have "(v, u) ∈ r⇧↓" unfolding ‹r⇧↔⇧* = r⇧↓› [symmetric]
using conversion_trans unfolding trans_def by best
then obtain v' where "(v, v') ∈ r⇧*" and "(u, v') ∈ r⇧*" by auto
from ‹(u, v') ∈ r⇧*› and ‹u ∈ NF r› have "u = v'" by (rule NF_not_suc)
from ‹(v, v') ∈ r⇧*› and ‹v ∈ NF r› have "v = v'" by (rule NF_not_suc)
then show "u = v" unfolding ‹u = v'› by simp
qed
next
assume equal_NF:"∀u v. (x, u) ∈ r⇧! ∧ (y, v) ∈ r⇧! ⟶ u = v"
from ‹WN r› obtain u where "(x, u) ∈ r⇧!" by auto
from ‹WN r› obtain v where "(y, v) ∈ r⇧!" by auto
from ‹(x, u) ∈ r⇧!› and ‹(y, v) ∈ r⇧!› have "u = v" using equal_NF by simp
from ‹(x, u) ∈ r⇧!› and ‹(y, v) ∈ r⇧!› have "(x, v) ∈ r⇧*" and "(y, v) ∈ r⇧*"
unfolding ‹u = v› by auto
then have "(x, v) ∈ r⇧↔⇧*" and "(y, v) ∈ r⇧↔⇧*" by auto
from ‹(y, v) ∈ r⇧↔⇧*› have "(v, y) ∈ r⇧↔⇧*" using conversion_sym unfolding sym_def by best
with ‹(x, v) ∈ r⇧↔⇧*› show "(x, y) ∈ r⇧↔⇧*" using conversion_trans unfolding trans_def by best
qed
qed
lemma CR_imp_UNC:
assumes "CR r" shows "UNC r"
proof - {
fix x y assume "x ∈ NF r" and "y ∈ NF r" and "(x, y) ∈ r⇧↔⇧*"
have "r⇧↔⇧* = r⇧↓" by (rule CR_imp_conversionIff_join [OF assms])
from ‹(x, y) ∈ r⇧↔⇧*› have "(x, y) ∈ r⇧↓" unfolding ‹r⇧↔⇧* = r⇧↓› by simp
then obtain x' where "(x, x') ∈ r⇧*" and "(y, x') ∈ r⇧*" by best
from ‹(x, x') ∈ r⇧*› and ‹x ∈ NF r› have "x = x'" by (rule NF_not_suc)
from ‹(y, x') ∈ r⇧*› and ‹y ∈ NF r› have "y = x'" by (rule NF_not_suc)
then have "x = y" unfolding ‹x = x'› by simp
} then show ?thesis by (auto simp: UNC_def)
qed
lemma WN_UNF_imp_CR:
assumes "WN r" and "UNF r" shows "CR r"
proof - {
fix x y z assume "(x, y) ∈ r⇧*" and "(x, z) ∈ r⇧*"
from assms obtain y' where "(y, y') ∈ r⇧!" unfolding WN_defs by best
with ‹(x, y) ∈ r⇧*› have "(x, y') ∈ r⇧!" by auto
from assms obtain z' where "(z, z') ∈ r⇧!" unfolding WN_defs by best
with ‹(x, z) ∈ r⇧*› have "(x, z') ∈ r⇧!" by auto
with ‹(x, y') ∈ r⇧!› have "y' = z'" using ‹UNF r› unfolding UNF_defs by auto
from ‹(y, y') ∈ r⇧!› and ‹(z, z') ∈ r⇧!› have "(y, z) ∈ r⇧↓" unfolding ‹y' = z'› by auto
} then show ?thesis by auto
qed
definition diamond :: "'a rel ⇒ bool" ("◇") where
"◇ r ⟷ (r¯ O r) ⊆ (r O r¯)"
lemma diamond_I [intro]: "(r¯ O r) ⊆ (r O r¯) ⟹ ◇ r" unfolding diamond_def by simp
lemma diamond_E [elim]: "◇ r ⟹ ((r¯ O r) ⊆ (r O r¯) ⟹ P) ⟹ P"
unfolding diamond_def by simp
lemma diamond_imp_semi_confluence:
assumes "◇ r" shows "(r¯ O r⇧*) ⊆ r⇧↓"
proof (rule subrelI)
fix y z assume "(y, z) ∈ r¯ O r⇧*"
then obtain x where "(x, y) ∈ r" and "(x, z) ∈ r⇧*" by best
then obtain n where "(x, z) ∈ r^^n" using rtrancl_imp_UN_relpow by best
with ‹(x, y) ∈ r› show "(y, z) ∈ r⇧↓"
proof (induct n arbitrary: x z y)
case 0 then show ?case by auto
next
case (Suc n)
from ‹(x, z) ∈ r^^Suc n› obtain x' where "(x, x') ∈ r" and "(x', z) ∈ r^^n"
using relpow_Suc_D2 by best
with ‹(x, y) ∈ r› have "(y, x') ∈ (r¯ O r)" by auto
with ‹◇ r› have "(y, x') ∈ (r O r¯)" by auto
then obtain y' where "(x', y') ∈ r" and "(y, y') ∈ r" by best
with Suc and ‹(x', z) ∈ r^^n› have "(y', z) ∈ r⇧↓" by auto
with ‹(y, y') ∈ r› show ?case by (auto intro: rtrancl_join_join)
qed
qed
lemma semi_confluence_imp_CR:
assumes "(r¯ O r⇧*) ⊆ r⇧↓" shows "CR r"
proof - {
fix x y z assume "(x, y) ∈ r⇧*" and "(x, z) ∈ r⇧*"
then obtain n where "(x, z) ∈ r^^n" using rtrancl_imp_UN_relpow by best
with ‹(x, y) ∈ r⇧*› have "(y, z) ∈ r⇧↓"
proof (induct n arbitrary: x y z)
case 0 then show ?case by auto
next
case (Suc n)
from ‹(x, z) ∈ r^^Suc n› obtain x' where "(x, x') ∈ r" and "(x', z) ∈ r^^n"
using relpow_Suc_D2 by best
from ‹(x, x') ∈ r› and ‹(x, y) ∈ r⇧*› have "(x', y) ∈ (r¯ O r⇧* )" by auto
with assms have "(x', y) ∈ r⇧↓" by auto
then obtain y' where "(x', y') ∈ r⇧*" and "(y, y') ∈ r⇧*" by best
with Suc and ‹(x', z) ∈ r^^n› have "(y', z) ∈ r⇧↓" by simp
then obtain u where "(z, u) ∈ r⇧*" and "(y', u) ∈ r⇧*" by best
from ‹(y, y') ∈ r⇧*› and ‹(y', u) ∈ r⇧*› have "(y, u) ∈ r⇧*" by auto
with ‹(z, u) ∈ r⇧*› show ?case by best
qed
} then show ?thesis by auto
qed
lemma diamond_imp_CR:
assumes "◇ r" shows "CR r"
using assms by (rule diamond_imp_semi_confluence [THEN semi_confluence_imp_CR])
lemma diamond_imp_CR':
assumes "◇ s" and "r ⊆ s" and "s ⊆ r⇧*" shows "CR r"
unfolding CR_iff_meet_subset_join
proof -
from ‹◇ s› have "CR s" by (rule diamond_imp_CR)
then have "s⇧↑ ⊆ s⇧↓" unfolding CR_iff_meet_subset_join by simp
from ‹r ⊆ s› have "r⇧* ⊆ s⇧*" by (rule rtrancl_mono)
from ‹s ⊆ r⇧*› have "s⇧* ⊆ (r⇧*)⇧*" by (rule rtrancl_mono)
then have "s⇧* ⊆ r⇧*" by simp
with ‹r⇧* ⊆ s⇧*› have "r⇧* = s⇧*" by simp
show "r⇧↑ ⊆ r⇧↓" unfolding meet_def join_def rtrancl_converse ‹r⇧* = s⇧*›
unfolding rtrancl_converse [symmetric] meet_def [symmetric]
join_def [symmetric] by (rule ‹s⇧↑ ⊆ s⇧↓›)
qed
lemma SN_imp_minimal:
assumes "SN A"
shows "∀Q x. x ∈ Q ⟶ (∃z∈Q. ∀y. (z, y) ∈ A ⟶ y ∉ Q)"
proof (rule ccontr)
assume "¬ (∀Q x. x ∈ Q ⟶ (∃z∈Q. ∀y. (z, y) ∈ A ⟶ y ∉ Q))"
then obtain Q x where "x ∈ Q" and "∀z∈Q. ∃y. (z, y) ∈ A ∧ y ∈ Q" by auto
then have "∀z. ∃y. z ∈ Q ⟶ (z, y) ∈ A ∧ y ∈ Q" by auto
then have "∃f. ∀x. x ∈ Q ⟶ (x, f x) ∈ A ∧ f x ∈ Q" by (rule choice)
then obtain f where a:"∀x. x ∈ Q ⟶ (x, f x) ∈ A ∧ f x ∈ Q" (is "∀x. ?P x") by best
let ?S = "λi. (f ^^ i) x"
have "?S 0 = x" by simp
have "∀i. (?S i, ?S (Suc i)) ∈ A ∧ ?S (Suc i) ∈ Q"
proof
fix i show "(?S i, ?S (Suc i)) ∈ A ∧ ?S (Suc i) ∈ Q"
by (induct i) (auto simp: ‹x ∈ Q› a)
qed
with ‹?S 0 = x› have "∃S. S 0 = x ∧ chain A S" by fast
with assms show False by auto
qed
lemma SN_on_imp_on_minimal:
assumes "SN_on r {x}"
shows "∀Q. x ∈ Q ⟶ (∃z∈Q. ∀y. (z, y) ∈ r ⟶ y ∉ Q)"
proof (rule ccontr)
assume "¬(∀Q. x ∈ Q ⟶ (∃z∈Q. ∀y. (z, y) ∈ r ⟶ y ∉ Q))"
then obtain Q where "x ∈ Q" and "∀z∈Q. ∃y. (z, y) ∈ r ∧ y ∈ Q" by auto
then have "∀z. ∃y. z ∈ Q ⟶ (z, y) ∈ r ∧ y ∈ Q" by auto
then have "∃f. ∀x. x ∈ Q ⟶ (x, f x) ∈ r ∧ f x ∈ Q" by (rule choice)
then obtain f where a: "∀x. x ∈ Q ⟶ (x, f x) ∈ r ∧ f x ∈ Q" (is "∀x. ?P x") by best
let ?S = "λi. (f ^^ i) x"
have "?S 0 = x" by simp
have "∀i. (?S i,?S(Suc i)) ∈ r ∧ ?S(Suc i) ∈ Q"
proof
fix i show "(?S i,?S(Suc i)) ∈ r ∧ ?S(Suc i) ∈ Q" by (induct i) (auto simp:‹x ∈ Q› a)
qed
with ‹?S 0 = x› have "∃S. S 0 = x ∧ chain r S" by fast
with assms show False by auto
qed
lemma minimal_imp_wf:
assumes "∀Q x. x ∈ Q ⟶ (∃z∈Q. ∀y. (z, y) ∈ r ⟶ y ∉ Q)"
shows "wf(r¯)"
proof (rule ccontr)
assume "¬ wf(r¯)"
then have "∃P. (∀x. (∀y. (x, y) ∈ r ⟶ P y) ⟶ P x) ∧ (∃x. ¬ P x)" unfolding wf_def by simp
then obtain P x where suc:"∀x. (∀y. (x, y) ∈ r ⟶ P y) ⟶ P x" and "¬ P x" by auto
let ?Q = "{x. ¬ P x}"
from ‹¬ P x› have "x ∈ ?Q" by simp
from assms have "∀x. x ∈ ?Q ⟶ (∃z∈?Q. ∀y. (z, y) ∈ r ⟶ y ∉ ?Q)" by (rule allE [where x = ?Q])
with ‹x ∈ ?Q› obtain z where "z ∈ ?Q" and min:" ∀y. (z, y) ∈ r ⟶ y ∉ ?Q" by best
from ‹z ∈ ?Q› have "¬ P z" by simp
with suc obtain y where "(z, y) ∈ r" and "¬ P y" by best
then have "y ∈ ?Q" by simp
with ‹(z, y) ∈ r› and min show False by simp
qed
lemmas SN_imp_wf = SN_imp_minimal [THEN minimal_imp_wf]
lemma wf_imp_SN:
assumes "wf (A¯)" shows "SN A"
proof - {
fix a
let ?P = "λa. ¬(∃S. S 0 = a ∧ chain A S)"
from ‹wf (A¯)› have "?P a"
proof induct
case (less a)
then have IH: "⋀b. (a, b) ∈ A ⟹ ?P b" by auto
show "?P a"
proof (rule ccontr)
assume "¬ ?P a"
then obtain S where "S 0 = a" and "chain A S" by auto
then have "(S 0, S 1) ∈ A" by auto
with IH have "?P (S 1)" unfolding ‹S 0 = a› by auto
with ‹chain A S› show False by auto
qed
qed
then have "SN_on A {a}" unfolding SN_defs by auto
} then show ?thesis by fast
qed
lemma SN_nat_gt: "SN {(a, b :: nat) . a > b}"
proof -
from wf_less have "wf ({(x, y) . (x :: nat) > y}¯)" unfolding converse_unfold by auto
from wf_imp_SN [OF this] show ?thesis .
qed
lemma SN_iff_wf: "SN A = wf (A¯)" by (auto simp: SN_imp_wf wf_imp_SN)
lemma SN_imp_acyclic: "SN R ⟹ acyclic R"
using wf_acyclic [of "R¯", unfolded SN_iff_wf [symmetric]] by auto
lemma SN_induct:
assumes sn: "SN r" and step: "⋀a. (⋀b. (a, b) ∈ r ⟹ P b) ⟹ P a"
shows "P a"
using sn unfolding SN_iff_wf proof induct
case (less a)
with step show ?case by best
qed
lemmas SN_induct_rule = SN_induct [consumes 1, case_names IH, induct pred: SN]
lemma SN_on_induct [consumes 2, case_names IH, induct pred: SN_on]:
assumes SN: "SN_on R A"
and "s ∈ A"
and imp: "⋀t. (⋀u. (t, u) ∈ R ⟹ P u) ⟹ P t"
shows "P s"
proof -
let ?R = "restrict_SN R R"
let ?P = "λt. SN_on R {t} ⟶ P t"
have "SN_on R {s} ⟶ P s"
proof (rule SN_induct [OF SN_restrict_SN_idemp [of R], of ?P])
fix a
assume ind: "⋀b. (a, b) ∈ ?R ⟹ SN_on R {b} ⟶ P b"
show "SN_on R {a} ⟶ P a"
proof
assume SN: "SN_on R {a}"
show "P a"
proof (rule imp)
fix b
assume "(a, b) ∈ R"
with SN step_preserves_SN_on [OF this SN]
show "P b" using ind [of b] unfolding restrict_SN_def by auto
qed
qed
qed
with SN show "P s" using ‹s ∈ A› unfolding SN_on_def by blast
qed
lemma accp_imp_SN_on:
assumes "⋀x. x ∈ A ⟹ Wellfounded.accp g x"
shows "SN_on {(y, z). g z y} A"
proof - {
fix x assume "x ∈ A"
from assms [OF this]
have "SN_on {(y, z). g z y} {x}"
proof (induct rule: accp.induct)
case (accI x)
show ?case
proof
fix f
assume x: "f 0 ∈ {x}" and steps: "∀ i. (f i, f (Suc i)) ∈ {a. (λ(y, z). g z y) a}"
then have "g (f 1) x" by auto
from accI(2)[OF this] steps x show False unfolding SN_on_def by auto
qed
qed
}
then show ?thesis unfolding SN_on_def by blast
qed
lemma SN_on_imp_accp:
assumes "SN_on {(y, z). g z y} A"
shows "∀x∈A. Wellfounded.accp g x"
proof
fix x assume "x ∈ A"
with assms show "Wellfounded.accp g x"
proof (induct rule: SN_on_induct)
case (IH x)
show ?case
proof
fix y
assume "g y x"
with IH show "Wellfounded.accp g y" by simp
qed
qed
qed
lemma SN_on_conv_accp:
"SN_on {(y, z). g z y} {x} = Wellfounded.accp g x"
using SN_on_imp_accp [of g "{x}"]
accp_imp_SN_on [of "{x}" g]
by auto
lemma SN_on_conv_acc: "SN_on {(y, z). (z, y) ∈ r} {x} ⟷ x ∈ Wellfounded.acc r"
unfolding SN_on_conv_accp accp_acc_eq ..
lemma acc_imp_SN_on:
assumes "x ∈ Wellfounded.acc r" shows "SN_on {(y, z). (z, y) ∈ r} {x}"
using assms unfolding SN_on_conv_acc by simp
lemma SN_on_imp_acc:
assumes "SN_on {(y, z). (z, y) ∈ r} {x}" shows "x ∈ Wellfounded.acc r"
using assms unfolding SN_on_conv_acc by simp
subsection ‹Newman's Lemma›
lemma rtrancl_len_E [elim]:
assumes "(x, y) ∈ r⇧*" obtains n where "(x, y) ∈ r^^n"
using rtrancl_imp_UN_relpow [OF assms] by best
lemma relpow_Suc_E2' [elim]:
assumes "(x, z) ∈ A^^Suc n" obtains y where "(x, y) ∈ A" and "(y, z) ∈ A⇧*"
proof -
assume assm: "⋀y. (x, y) ∈ A ⟹ (y, z) ∈ A⇧* ⟹ thesis"
from relpow_Suc_E2 [OF assms] obtain y where "(x, y) ∈ A" and "(y, z) ∈ A^^n" by auto
then have "(y, z) ∈ A⇧*" using relpow_imp_rtrancl by auto
from assm [OF ‹(x, y) ∈ A› this] show thesis .
qed
lemmas SN_on_induct' [consumes 1, case_names IH] = SN_on_induct [OF _ singletonI]
lemma Newman_local:
assumes "SN_on r X" and WCR: "WCR_on r {x. SN_on r {x}}"
shows "CR_on r X"
proof - {
fix x
assume "x ∈ X"
with assms have "SN_on r {x}" unfolding SN_on_def by auto
with this have "CR_on r {x}"
proof (induct rule: SN_on_induct')
case (IH x) show ?case
proof
fix y z assume "(x, y) ∈ r⇧*" and "(x, z) ∈ r⇧*"
from ‹(x, y) ∈ r⇧*› obtain m where "(x, y) ∈ r^^m" ..
from ‹(x, z) ∈ r⇧*› obtain n where "(x, z) ∈ r^^n" ..
show "(y, z) ∈ r⇧↓"
proof (cases n)
case 0
from ‹(x, z) ∈ r^^n› have eq: "x = z" by (simp add: 0)
from ‹(x, y) ∈ r⇧*› show ?thesis unfolding eq ..
next
case (Suc n')
from ‹(x, z) ∈ r^^n› [unfolded Suc] obtain t where "(x, t) ∈ r" and "(t, z) ∈ r⇧*" ..
show ?thesis
proof (cases m)
case 0
from ‹(x, y) ∈ r^^m› have eq: "x = y" by (simp add: 0)
from ‹(x, z) ∈ r⇧*› show ?thesis unfolding eq ..
next
case (Suc m')
from ‹(x, y) ∈ r^^m› [unfolded Suc] obtain s where "(x, s) ∈ r" and "(s, y) ∈ r⇧*" ..
from WCR IH(2) have "WCR_on r {x}" unfolding WCR_on_def by auto
with ‹(x, s) ∈ r› and ‹(x, t) ∈ r› have "(s, t) ∈ r⇧↓" by auto
then obtain u where "(s, u) ∈ r⇧*" and "(t, u) ∈ r⇧*" ..
from ‹(x, s) ∈ r› IH(2) have "SN_on r {s}" by (rule step_preserves_SN_on)
from IH(1)[OF ‹(x, s) ∈ r› this] have "CR_on r {s}" .
from this and ‹(s, u) ∈ r⇧*› and ‹(s, y) ∈ r⇧*› have "(u, y) ∈ r⇧↓" by auto
then obtain v where "(u, v) ∈ r⇧*" and "(y, v) ∈ r⇧*" ..
from ‹(x, t) ∈ r› IH(2) have "SN_on r {t}" by (rule step_preserves_SN_on)
from IH(1)[OF ‹(x, t) ∈ r› this] have "CR_on r {t}" .
moreover from ‹(t, u) ∈ r⇧*› and ‹(u, v) ∈ r⇧*› have "(t, v) ∈ r⇧*" by auto
ultimately have "(z, v) ∈ r⇧↓" using ‹(t, z) ∈ r⇧*› by auto
then obtain w where "(z, w) ∈ r⇧*" and "(v, w) ∈ r⇧*" ..
from ‹(y, v) ∈ r⇧*› and ‹(v, w) ∈ r⇧*› have "(y, w) ∈ r⇧*" by auto
with ‹(z, w) ∈ r⇧*› show ?thesis by auto
qed
qed
qed
qed
}
then show ?thesis unfolding CR_on_def by blast
qed
lemma Newman: "SN r ⟹ WCR r ⟹ CR r"
using Newman_local [of r UNIV]
unfolding WCR_on_def by auto
lemma Image_SN_on:
assumes "SN_on r (r `` A)"
shows "SN_on r A"
proof
fix f
assume "f 0 ∈ A" and chain: "chain r f"
then have "f (Suc 0) ∈ r `` A" by auto
with assms have "SN_on r {f (Suc 0)}" by (auto simp add: ‹f 0 ∈ A› SN_defs)
moreover have "¬ SN_on r {f (Suc 0)}"
proof -
have "f (Suc 0) ∈ {f (Suc 0)}" by simp
moreover from chain have "chain r (f ∘ Suc)" by auto
ultimately show ?thesis by auto
qed
ultimately show False by simp
qed
lemma SN_on_Image_conv: "SN_on r (r `` A) = SN_on r A"
using SN_on_Image and Image_SN_on by blast
text ‹If all successors are terminating, then the current element is also terminating.›
lemma step_reflects_SN_on:
assumes "(⋀b. (a, b) ∈ r ⟹ SN_on r {b})"
shows "SN_on r {a}"
using assms and Image_SN_on [of r "{a}"] by (auto simp: SN_defs)
lemma SN_on_all_reducts_SN_on_conv:
"SN_on r {a} = (∀b. (a, b) ∈ r ⟶ SN_on r {b})"
using SN_on_Image_conv [of r "{a}"] by (auto simp: SN_defs)
lemma SN_imp_SN_trancl: "SN R ⟹ SN (R⇧+)"
unfolding SN_iff_wf by (rule wf_converse_trancl)
lemma SN_trancl_imp_SN:
assumes "SN (R⇧+)" shows "SN R"
using assms by (rule SN_on_trancl_imp_SN_on)
lemma SN_trancl_SN_conv: "SN (R⇧+) = SN R"
using SN_trancl_imp_SN [of R] SN_imp_SN_trancl [of R] by blast
lemma SN_inv_image: "SN R ⟹ SN (inv_image R f)" unfolding SN_iff_wf by simp
lemma SN_subset: "SN R ⟹ R' ⊆ R ⟹ SN R'" unfolding SN_defs by blast
lemma SN_pow_imp_SN:
assumes "SN (A^^Suc n)" shows "SN A"
proof (rule ccontr)
assume "¬ SN A"
then obtain S where "chain A S" unfolding SN_defs by auto
from chain_imp_relpow [OF this]
have step: "⋀i. (S i, S (i + (Suc n))) ∈ A^^Suc n" .
let ?T = "λi. S (i * (Suc n))"
have "chain (A^^Suc n) ?T"
proof
fix i show "(?T i, ?T (Suc i)) ∈ A^^Suc n" unfolding mult_Suc
using step [of "i * Suc n"] by (simp only: add.commute)
qed
then have "¬ SN (A^^Suc n)" unfolding SN_defs by fast
with assms show False by simp
qed
lemma pow_Suc_subset_trancl: "R^^(Suc n) ⊆ R⇧+"
using trancl_power [of _ R] by blast
lemma SN_imp_SN_pow:
assumes "SN R" shows "SN (R^^Suc n)"
using SN_subset [where R="R⇧+", OF SN_imp_SN_trancl [OF assms] pow_Suc_subset_trancl] by simp
lemma SN_pow: "SN R ⟷ SN (R ^^ Suc n)"
by (rule iffI, rule SN_imp_SN_pow, assumption, rule SN_pow_imp_SN, assumption)
lemma SN_on_trancl:
assumes "SN_on r A" shows "SN_on (r⇧+) A"
using assms
proof (rule contrapos_pp)
let ?r = "restrict_SN r r"
assume "¬ SN_on (r⇧+) A"
then obtain f where "f 0 ∈ A" and chain: "chain (r⇧+) f" by auto
have "SN ?r" by (rule SN_restrict_SN_idemp)
then have "SN (?r⇧+)" by (rule SN_imp_SN_trancl)
have "∀i. (f 0, f i) ∈ r⇧*"
proof
fix i show "(f 0, f i) ∈ r⇧*"
proof (induct i)
case 0 show ?case ..
next
case (Suc i)
from chain have "(f i, f (Suc i)) ∈ r⇧+" ..
with Suc show ?case by auto
qed
qed
with assms have "∀i. SN_on r {f i}"
using steps_preserve_SN_on [of "f 0" _ r]
and ‹f 0 ∈ A›
and SN_on_subset2 [of "{f 0}" "A"] by auto
with chain have "chain (?r⇧+) f"
unfolding restrict_SN_trancl_simp
unfolding restrict_SN_def by auto
then have "¬ SN_on (?r⇧+) {f 0}" by auto
with ‹SN (?r⇧+)› have False by (simp add: SN_defs)
then show "¬ SN_on r A" by simp
qed
lemma SN_on_trancl_SN_on_conv: "SN_on (R⇧+) T = SN_on R T"
using SN_on_trancl_imp_SN_on [of R] SN_on_trancl [of R] by blast
text ‹Restrict an ARS to elements of a given set.›
definition "restrict" :: "'a rel ⇒ 'a set ⇒ 'a rel" where
"restrict r S = {(x, y). x ∈ S ∧ y ∈ S ∧ (x, y) ∈ r}"
lemma SN_on_restrict:
assumes "SN_on r A"
shows "SN_on (restrict r S) A" (is "SN_on ?r A")
proof (rule ccontr)
assume "¬ SN_on ?r A"
then have "∃f. f 0 ∈ A ∧ chain ?r f" by auto
then have "∃f. f 0 ∈ A ∧ chain r f" unfolding restrict_def by auto
with ‹SN_on r A› show False by auto
qed
lemma restrict_rtrancl: "(restrict r S)⇧* ⊆ r⇧*" (is "?r⇧* ⊆ r⇧*")
proof - {
fix x y assume "(x, y) ∈ ?r⇧*" then have "(x, y) ∈ r⇧*" unfolding restrict_def by induct auto
} then show ?thesis by auto
qed
lemma rtrancl_Image_step:
assumes "a ∈ r⇧* `` A"
and "(a, b) ∈ r⇧*"
shows "b ∈ r⇧* `` A"
proof -
from assms(1) obtain c where "c ∈ A" and "(c, a) ∈ r⇧*" by auto
with assms have "(c, b) ∈ r⇧*" by auto
with ‹c ∈ A› show ?thesis by auto
qed
lemma WCR_SN_on_imp_CR_on:
assumes "WCR r" and "SN_on r A" shows "CR_on r A"
proof -
let ?S = "r⇧* `` A"
let ?r = "restrict r ?S"
have "∀x. SN_on ?r {x}"
proof
fix y have "y ∉ ?S ∨ y ∈ ?S" by simp
then show "SN_on ?r {y}"
proof
assume "y ∉ ?S" then show ?thesis unfolding restrict_def by auto
next
assume "y ∈ ?S"
then have "y ∈ r⇧* `` A" by simp
with SN_on_Image_rtrancl [OF ‹SN_on r A›]
have "SN_on r {y}" using SN_on_subset2 [of "{y}" "r⇧* `` A"] by blast
then show ?thesis by (rule SN_on_restrict)
qed
qed
then have "SN ?r" unfolding SN_defs by auto
{
fix x y assume "(x, y) ∈ r⇧*" and "x ∈ ?S" and "y ∈ ?S"
then obtain n where "(x, y) ∈ r^^n" and "x ∈ ?S" and "y ∈ ?S"
using rtrancl_imp_UN_relpow by best
then have "(x, y) ∈ ?r⇧*"
proof (induct n arbitrary: x y)
case 0 then show ?case by simp
next
case (Suc n)
from ‹(x, y) ∈ r^^Suc n› obtain x' where "(x, x') ∈ r" and "(x', y) ∈ r^^n"
using relpow_Suc_D2 by best
then have "(x, x') ∈ r⇧*" by simp
with ‹x ∈ ?S› have "x' ∈ ?S" by (rule rtrancl_Image_step)
with Suc and ‹(x', y) ∈ r^^n› have "(x', y) ∈ ?r⇧*" by simp
from ‹(x, x') ∈ r› and ‹x ∈ ?S› and ‹x' ∈ ?S› have "(x, x') ∈ ?r"
unfolding restrict_def by simp
with ‹(x', y) ∈ ?r⇧*› show ?case by simp
qed
}
then have a:"∀x y. (x, y) ∈ r⇧* ∧ x ∈ ?S ∧ y ∈ ?S ⟶ (x, y) ∈ ?r⇧*" by simp
{
fix x' y z assume "(x', y) ∈ ?r" and "(x', z) ∈ ?r"
then have "x' ∈ ?S" and "y ∈ ?S" and "z ∈ ?S" and "(x', y) ∈ r" and "(x', z) ∈ r"
unfolding restrict_def by auto
with ‹WCR r› have "(y, z) ∈ r⇧↓" by auto
then obtain u where "(y, u) ∈ r⇧*" and "(z, u) ∈ r⇧*" by auto
from ‹x' ∈ ?S› obtain x where "x ∈ A" and "(x, x') ∈ r⇧*" by auto
from ‹(x', y) ∈ r› have "(x', y) ∈ r⇧*" by auto
with ‹(y, u) ∈ r⇧*› have "(x', u) ∈ r⇧*" by auto
with ‹(x, x') ∈ r⇧*› have "(x, u) ∈ r⇧*" by simp
then have "u ∈ ?S" using ‹x ∈ A› by auto
from ‹y ∈ ?S› and ‹u ∈ ?S› and ‹(y, u) ∈ r⇧*› have "(y, u) ∈ ?r⇧*" using a by auto
from ‹z ∈ ?S› and ‹u ∈ ?S› and ‹(z, u) ∈ r⇧*› have "(z, u) ∈ ?r⇧*" using a by auto
with ‹(y, u) ∈ ?r⇧*› have "(y, z) ∈ ?r⇧↓" by auto
}
then have "WCR ?r" by auto
have "CR ?r" using Newman [OF ‹SN ?r› ‹WCR ?r›] by simp
{
fix x y z assume "x ∈ A" and "(x, y) ∈ r⇧*" and "(x, z) ∈ r⇧*"
then have "y ∈ ?S" and "z ∈ ?S" by auto
have "x ∈ ?S" using ‹x ∈ A› by auto
from a and ‹(x, y) ∈ r⇧*› and ‹x ∈ ?S› and ‹y ∈ ?S› have "(x, y) ∈ ?r⇧*" by simp
from a and ‹(x, z) ∈ r⇧*› and ‹x ∈ ?S› and ‹z ∈ ?S› have "(x, z) ∈ ?r⇧*" by simp
with ‹CR ?r› and ‹(x, y) ∈ ?r⇧*› have "(y, z) ∈ ?r⇧↓" by auto
then obtain u where "(y, u) ∈ ?r⇧*" and "(z, u) ∈ ?r⇧*" by best
then have "(y, u) ∈ r⇧*" and "(z, u) ∈ r⇧*" using restrict_rtrancl by auto
then have "(y, z) ∈ r⇧↓" by auto
}
then show ?thesis by auto
qed
lemma SN_on_Image_normalizable:
assumes "SN_on r A"
shows "∀a∈A. ∃b. b ∈ r⇧! `` A"
proof
fix a assume a: "a ∈ A"
show "∃b. b ∈ r⇧! `` A"
proof (rule ccontr)
assume "¬ (∃b. b ∈ r⇧! `` A)"
then have A: "∀b. (a, b) ∈ r⇧* ⟶ b ∉ NF r" using a by auto
then have "a ∉ NF r" by auto
let ?Q = "{c. (a, c) ∈ r⇧* ∧ c ∉ NF r}"
have "a ∈ ?Q" using ‹a ∉ NF r› by simp
have "∀c∈?Q. ∃b. (c, b) ∈ r ∧ b ∈ ?Q"
proof
fix c
assume "c ∈ ?Q"
then have "(a, c) ∈ r⇧*" and "c ∉ NF r" by auto
then obtain d where "(c, d) ∈ r" by auto
with ‹(a, c) ∈ r⇧*› have "(a, d) ∈ r⇧*" by simp
with A have "d ∉ NF r" by simp
with ‹(c, d) ∈ r› and ‹(a, c) ∈ r⇧*›
show "∃b. (c, b) ∈ r ∧ b ∈ ?Q" by auto
qed
with ‹a ∈ ?Q› have "a ∈ ?Q ∧ (∀c∈?Q. ∃b. (c, b) ∈ r ∧ b ∈ ?Q)" by auto
then have "∃Q. a ∈ Q ∧ (∀c∈Q. ∃b. (c, b) ∈ r ∧ b ∈ Q)" by (rule exI [of _ "?Q"])
then have "¬ (∀Q. a ∈ Q ⟶ (∃c∈Q. ∀b. (c, b) ∈ r ⟶ b ∉ Q))" by simp
with SN_on_imp_on_minimal [of r a] have "¬ SN_on r {a}" by blast
with assms and ‹a ∈ A› and SN_on_subset2 [of "{a}" A r] show False by simp
qed
qed
lemma SN_on_imp_normalizability:
assumes "SN_on r {a}" shows "∃b. (a, b) ∈ r⇧!"
using SN_on_Image_normalizable [OF assms] by auto
subsection ‹Commutation›
definition commute :: "'a rel ⇒ 'a rel ⇒ bool" where
"commute r s ⟷ ((r¯)⇧* O s⇧*) ⊆ (s⇧* O (r¯)⇧*)"
lemma CR_iff_self_commute: "CR r = commute r r"
unfolding commute_def CR_iff_meet_subset_join meet_def join_def
by simp
lemma rtrancl_imp_rtrancl_UN:
assumes "(x, y) ∈ r⇧*" and "r ∈ I"
shows "(x, y) ∈ (⋃r∈I. r)⇧*" (is "(x, y) ∈ ?r⇧*")
using assms proof induct
case base then show ?case by simp
next
case (step y z)
then have "(x, y) ∈ ?r⇧*" by simp
from ‹(y, z) ∈ r› and ‹r ∈ I› have "(y, z) ∈ ?r⇧*" by auto
with ‹(x, y) ∈ ?r⇧*› show ?case by auto
qed
definition quasi_commute :: "'a rel ⇒ 'a rel ⇒ bool" where
"quasi_commute r s ⟷ (s O r) ⊆ r O (r ∪ s)⇧*"
lemma rtrancl_union_subset_rtrancl_union_trancl: "(r ∪ s⇧+)⇧* = (r ∪ s)⇧*"
proof
show "(r ∪ s⇧+)⇧* ⊆ (r ∪ s)⇧*"
proof (rule subrelI)
fix x y assume "(x, y) ∈ (r ∪ s⇧+)⇧*"
then show "(x, y) ∈ (r ∪ s)⇧*"
proof (induct)
case base then show ?case by auto
next
case (step y z)
then have "(y, z) ∈ r ∨ (y, z) ∈ s⇧+" by auto
then have "(y, z) ∈ (r ∪ s)⇧*"
proof
assume "(y, z) ∈ r" then show ?thesis by auto
next
assume "(y, z) ∈ s⇧+"
then have "(y, z) ∈ s⇧*" by auto
then have "(y, z) ∈ r⇧* ∪ s⇧*" by auto
then show ?thesis using rtrancl_Un_subset by auto
qed
with ‹(x, y) ∈ (r ∪ s)⇧*› show ?case by simp
qed
qed
next
show "(r ∪ s)⇧* ⊆ (r ∪ s⇧+)⇧*"
proof (rule subrelI)
fix x y assume "(x, y) ∈ (r ∪ s)⇧*"
then show "(x, y) ∈ (r ∪ s⇧+)⇧*"
proof (induct)
case base then show ?case by auto
next
case (step y z)
then have "(y, z) ∈ (r ∪ s⇧+)⇧*" by auto
with ‹(x, y) ∈ (r ∪ s⇧+)⇧*› show ?case by auto
qed
qed
qed
lemma qc_imp_qc_trancl:
assumes "quasi_commute r s" shows "quasi_commute r (s⇧+)"
unfolding quasi_commute_def
proof (rule subrelI)
fix x z assume "(x, z) ∈ s⇧+ O r"
then obtain y where "(x, y) ∈ s⇧+" and "(y, z) ∈ r" by best
then show "(x, z) ∈ r O (r ∪ s⇧+)⇧*"
proof (induct arbitrary: z)
case (base y)
then have "(x, z) ∈ (s O r)" by auto
with assms have "(x, z) ∈ r O (r ∪ s)⇧*" unfolding quasi_commute_def by auto
then show ?case using rtrancl_union_subset_rtrancl_union_trancl by auto
next
case (step a b)
then have "(a, z) ∈ (s O r)" by auto
with assms have "(a, z) ∈ r O (r ∪ s)⇧*" unfolding quasi_commute_def by auto
then obtain u where "(a, u) ∈ r" and "(u, z) ∈ (r ∪ s)⇧*" by best
then have "(u, z) ∈ (r ∪ s⇧+)⇧*" using rtrancl_union_subset_rtrancl_union_trancl by auto
from ‹(a, u) ∈ r› and step have "(x, u) ∈ r O (r ∪ s⇧+)⇧*" by auto
then obtain v where "(x, v) ∈ r" and "(v, u) ∈ (r ∪ s⇧+)⇧*" by best
with ‹(u, z) ∈ (r ∪ s⇧+)⇧*› have "(v, z) ∈ (r ∪ s⇧+)⇧*" by auto
with ‹(x, v) ∈ r› show ?case by auto
qed
qed
lemma steps_reflect_SN_on:
assumes "¬ SN_on r {b}" and "(a, b) ∈ r⇧*"
shows "¬ SN_on r {a}"
using SN_on_Image_rtrancl [of r "{a}"]
and assms and SN_on_subset2 [of "{b}" "r⇧* `` {a}" r] by blast
lemma chain_imp_not_SN_on:
assumes "chain r f"
shows "¬ SN_on r {f i}"
proof -
let ?f = "λj. f (i + j)"
have "?f 0 ∈ {f i}" by simp
moreover have "chain r ?f" using assms by auto
ultimately have "?f 0 ∈ {f i} ∧ chain r ?f" by blast
then have "∃g. g 0 ∈ {f i} ∧ chain r g" by (rule exI [of _ "?f"])
then show ?thesis unfolding SN_defs by auto
qed
lemma quasi_commute_imp_SN:
assumes "SN r" and "SN s" and "quasi_commute r s"
shows "SN (r ∪ s)"
proof -
have "quasi_commute r (s⇧+)" by (rule qc_imp_qc_trancl [OF ‹quasi_commute r s›])
let ?B = "{a. ¬ SN_on (r ∪ s) {a}}"
{
assume "¬ SN(r ∪ s)"
then obtain a where "a ∈ ?B" unfolding SN_defs by fast
from ‹SN r› have "∀Q x. x ∈ Q ⟶ (∃z∈Q. ∀y. (z, y) ∈ r ⟶ y ∉ Q)"
by (rule SN_imp_minimal)
then have "∀x. x ∈ ?B ⟶ (∃z∈?B. ∀y. (z, y) ∈ r ⟶ y ∉ ?B)" by (rule spec [where x = ?B])
with ‹a ∈ ?B› obtain b where "b ∈ ?B" and min: "∀y. (b, y) ∈ r ⟶ y ∉ ?B" by auto
from ‹b ∈ ?B› obtain S where "S 0 = b" and
chain: "chain (r ∪ s) S" unfolding SN_on_def by auto
let ?S = "λi. S(Suc i)"
have "?S 0 = S 1" by simp
from chain have "chain (r ∪ s) ?S" by auto
with ‹?S 0 = S 1› have "¬ SN_on (r ∪ s) {S 1}" unfolding SN_on_def by auto
from ‹S 0 = b› and chain have "(b, S 1) ∈ r ∪ s" by auto
with min and ‹¬ SN_on (r ∪ s) {S 1}› have "(b, S 1) ∈ s" by auto
let ?i = "LEAST i. (S i, S(Suc i)) ∉ s"
{
assume "chain s S"
with ‹S 0 = b› have "¬ SN_on s {b}" unfolding SN_on_def by auto
with ‹SN s› have False unfolding SN_defs by auto
}
then have ex: "∃i. (S i, S(Suc i)) ∉ s" by auto
then have "(S ?i, S(Suc ?i)) ∉ s" by (rule LeastI_ex)
with chain have "(S ?i, S(Suc ?i)) ∈ r" by auto
have ini: "∀i<?i. (S i, S(Suc i)) ∈ s" using not_less_Least by auto
{
fix i assume "i < ?i" then have "(b, S(Suc i)) ∈ s⇧+"
proof (induct i)
case 0 then show ?case using ‹(b, S 1) ∈ s› and ‹S 0 = b› by auto
next
case (Suc k)
then have "(b, S(Suc k)) ∈ s⇧+" and "Suc k < ?i" by auto
with ‹∀i<?i. (S i, S(Suc i)) ∈ s› have "(S(Suc k), S(Suc(Suc k))) ∈ s" by fast
with ‹(b, S(Suc k)) ∈ s⇧+› show ?case by auto
qed
}
then have pref: "∀i<?i. (b, S(Suc i)) ∈ s⇧+" by auto
from ‹(b, S 1) ∈ s› and ‹S 0 = b› have "(S 0, S(Suc 0)) ∈ s" by auto
{
assume "?i = 0"
from ex have "(S ?i, S(Suc ?i)) ∉ s" by (rule LeastI_ex)
with ‹(S 0, S(Suc 0)) ∈ s› have False unfolding ‹?i = 0› by simp
}
then have "0 < ?i" by auto
then obtain j where "?i = Suc j" unfolding gr0_conv_Suc by best
with ini have "(S(?i-Suc 0), S(Suc(?i-Suc 0))) ∈ s" by auto
with pref have "(b, S(Suc j)) ∈ s⇧+" unfolding ‹?i = Suc j› by auto
then have "(b, S ?i) ∈ s⇧+" unfolding ‹?i = Suc j› by auto
with ‹(S ?i, S(Suc ?i)) ∈ r› have "(b, S(Suc ?i)) ∈ (s⇧+ O r)" by auto
with ‹quasi_commute r (s⇧+)› have "(b, S(Suc ?i)) ∈ r O (r ∪ s⇧+)⇧*"
unfolding quasi_commute_def by auto
then obtain c where "(b, c) ∈ r" and "(c, S(Suc ?i)) ∈ (r ∪ s⇧+)⇧*" by best
from ‹(b, c) ∈ r› have "(b, c) ∈ (r ∪ s)⇧*" by auto
from chain_imp_not_SN_on [of S "r ∪ s"]
and chain have "¬ SN_on (r ∪ s) {S (Suc ?i)}" by auto
from ‹(c, S(Suc ?i)) ∈ (r ∪ s⇧+)⇧*› have "(c, S(Suc ?i)) ∈ (r ∪ s)⇧*"
unfolding rtrancl_union_subset_rtrancl_union_trancl by auto
with steps_reflect_SN_on [of "r ∪ s"]
and ‹¬ SN_on (r ∪ s) {S(Suc ?i)}› have "¬ SN_on (r ∪ s) {c}" by auto
then have "c ∈ ?B" by simp
with ‹(b, c) ∈ r› and min have False by auto
}
then show ?thesis by auto
qed
subsection ‹Strong Normalization›
lemma non_strict_into_strict:
assumes compat: "NS O S ⊆ S"
and steps: "(s, t) ∈ (NS⇧*) O S"
shows "(s, t) ∈ S"
using steps proof
fix x u z
assume "(s, t) = (x, z)" and "(x, u) ∈ NS⇧*" and "(u, z) ∈ S"
then have "(s, u) ∈ NS⇧*" and "(u, t) ∈ S" by auto
then show ?thesis
proof (induct rule:rtrancl.induct)
case (rtrancl_refl x) then show ?case .
next
case (rtrancl_into_rtrancl a b c)
with compat show ?case by auto
qed
qed
lemma comp_trancl:
assumes "R O S ⊆ S" shows "R O S⇧+ ⊆ S⇧+"
proof (rule subrelI)
fix w z assume "(w, z) ∈ R O S⇧+"
then obtain x where R_step: "(w, x) ∈ R" and S_seq: "(x, z) ∈ S⇧+" by best
from tranclD [OF S_seq] obtain y where S_step: "(x, y) ∈ S" and S_seq': "(y, z) ∈ S⇧*" by auto
from R_step and S_step have "(w, y) ∈ R O S" by auto
with assms have "(w, y) ∈ S" by auto
with S_seq' show "(w, z) ∈ S⇧+" by simp
qed
lemma comp_rtrancl_trancl:
assumes comp: "R O S ⊆ S"
and seq: "(s, t) ∈ (R ∪ S)⇧* O S"
shows "(s, t) ∈ S⇧+"
using seq proof
fix x u z
assume "(s, t) = (x, z)" and "(x, u) ∈ (R ∪ S)⇧*" and "(u, z) ∈ S"
then have "(s, u) ∈ (R ∪ S)⇧*" and "(u, t) ∈ S⇧+" by auto
then show ?thesis
proof (induct rule: rtrancl.induct)
case (rtrancl_refl x) then show ?case .
next
case (rtrancl_into_rtrancl a b c)
then have "(b, c) ∈ R ∪ S" by simp
then show ?case
proof
assume "(b, c) ∈ S"
with rtrancl_into_rtrancl
have "(b, t) ∈ S⇧+" by simp
with rtrancl_into_rtrancl show ?thesis by simp
next
assume "(b, c) ∈ R"
with comp_trancl [OF comp] rtrancl_into_rtrancl
show ?thesis by auto
qed
qed
qed
lemma trancl_union_right: "r⇧+ ⊆ (s ∪ r)⇧+"
proof (rule subrelI)
fix x y assume "(x, y) ∈ r⇧+" then show "(x, y) ∈ (s ∪ r)⇧+"
proof (induct)
case base then show ?case by auto
next
case (step a b)
then have "(a, b) ∈ (s ∪ r)⇧+" by auto
with ‹(x, a) ∈ (s ∪ r)⇧+› show ?case by auto
qed
qed
lemma restrict_SN_subset: "restrict_SN R S ⊆ R"
proof (rule subrelI)
fix a b assume "(a, b) ∈ restrict_SN R S" then show "(a, b) ∈ R" unfolding restrict_SN_def by simp
qed
lemma chain_Un_SN_on_imp_first_step:
assumes "chain (R ∪ S) t" and "SN_on S {t 0}"
shows "∃i. (t i, t (Suc i)) ∈ R ∧ (∀j<i. (t j, t (Suc j)) ∈ S ∧ (t j, t (Suc j)) ∉ R)"
proof -
from ‹SN_on S {t 0}› obtain i where "(t i, t (Suc i)) ∉ S" by blast
with assms have "(t i, t (Suc i)) ∈ R" (is "?P i") by auto
let ?i = "Least ?P"
from ‹?P i› have "?P ?i" by (rule LeastI)
have "∀j<?i. (t j, t (Suc j)) ∉ R" using not_less_Least by auto
moreover with assms have "∀j<?i. (t j, t (Suc j)) ∈ S" by best
ultimately have "∀j<?i. (t j, t (Suc j)) ∈ S ∧ (t j, t (Suc j)) ∉ R" by best
with ‹?P ?i› show ?thesis by best
qed
lemma first_step:
assumes C: "C = A ∪ B" and steps: "(x, y) ∈ C⇧*" and Bstep: "(y, z) ∈ B"
shows "∃y. (x, y) ∈ A⇧* O B"
using steps
proof (induct rule: converse_rtrancl_induct)
case base
show ?case using Bstep by auto
next
case (step u x)
from step(1)[unfolded C]
show ?case
proof
assume "(u, x) ∈ B"
then show ?thesis by auto
next
assume ux: "(u, x) ∈ A"
from step(3) obtain y where "(x, y) ∈ A⇧* O B" by auto
then obtain z where "(x, z) ∈ A⇧*" and step: "(z, y) ∈ B" by auto
with ux have "(u, z) ∈ A⇧*" by auto
with step have "(u, y) ∈ A⇧* O B" by auto
then show ?thesis by auto
qed
qed
lemma first_step_O:
assumes C: "C = A ∪ B" and steps: "(x, y) ∈ C⇧* O B"
shows "∃ y. (x, y) ∈ A⇧* O B"
proof -
from steps obtain z where "(x, z) ∈ C⇧*" and "(z, y) ∈ B" by auto
from first_step [OF C this] show ?thesis .
qed
lemma firstStep:
assumes LSR: "L = S ∪ R" and xyL: "(x, y) ∈ L⇧*"
shows "(x, y) ∈ R⇧* ∨ (x, y) ∈ R⇧* O S O L⇧*"
proof (cases "(x, y) ∈ R⇧*")
case True
then show ?thesis by simp
next
case False
let ?SR = "S ∪ R"
from xyL and LSR have "(x, y) ∈ ?SR⇧*" by simp
from this and False have "(x, y) ∈ R⇧* O S O ?SR⇧*"
proof (induct rule: rtrancl_induct)
case base then show ?case by simp
next
case (step y z)
then show ?case
proof (cases "(x, y) ∈ R⇧*")
case False with step have "(x, y) ∈ R⇧* O S O ?SR⇧*" by simp
from this obtain u where xu: "(x, u) ∈ R⇧* O S" and uy: "(u, y) ∈ ?SR⇧*" by force
from ‹(y, z) ∈ ?SR› have "(y, z) ∈ ?SR⇧*" by auto
with uy have "(u, z) ∈ ?SR⇧*" by (rule rtrancl_trans)
with xu show ?thesis by auto
next
case True
have "(y, z) ∈ S"
proof (rule ccontr)
assume "(y, z) ∉ S" with ‹(y, z) ∈ ?SR› have "(y, z) ∈ R" by auto
with True have "(x, z) ∈ R⇧*" by auto
with ‹(x, z) ∉ R⇧*› show False ..
qed
with True show ?thesis by auto
qed
qed
with LSR show ?thesis by simp
qed
lemma non_strict_ending:
assumes chain: "chain (R ∪ S) t"
and comp: "R O S ⊆ S"
and SN: "SN_on S {t 0}"
shows "∃j. ∀i≥j. (t i, t (Suc i)) ∈ R - S"
proof (rule ccontr)
assume "¬ ?thesis"
with chain have "∀i. ∃j. j ≥ i ∧ (t j, t (Suc j)) ∈ S" by blast
from choice [OF this] obtain f where S_steps: "∀i. i ≤ f i ∧ (t (f i), t (Suc (f i))) ∈ S" ..
let ?t = "λi. t (((Suc ∘ f) ^^ i) 0)"
have S_chain: "∀i. (t i, t (Suc (f i))) ∈ S⇧+"
proof
fix i
from S_steps have leq: "i≤f i" and step: "(t(f i), t(Suc(f i))) ∈ S" by auto
from chain_imp_rtrancl [OF chain leq] have "(t i, t(f i)) ∈ (R ∪ S)⇧*" .
with step have "(t i, t(Suc(f i))) ∈ (R ∪ S)⇧* O S" by auto
from comp_rtrancl_trancl [OF comp this] show "(t i, t(Suc(f i))) ∈ S⇧+" .
qed
then have "chain (S⇧+) ?t"by simp
moreover have "SN_on (S⇧+) {?t 0}" using SN_on_trancl [OF SN] by simp
ultimately show False unfolding SN_defs by best
qed
lemma SN_on_subset1:
assumes "SN_on r A" and "s ⊆ r"
shows "SN_on s A"
using assms unfolding SN_defs by blast
lemmas SN_on_mono = SN_on_subset1
lemma rtrancl_fun_conv:
"((s, t) ∈ R⇧*) = (∃ f n. f 0 = s ∧ f n = t ∧ (∀ i < n. (f i, f (Suc i)) ∈ R))"
unfolding rtrancl_is_UN_relpow using relpow_fun_conv [where R = R]
by auto
lemma compat_tr_compat:
assumes "NS O S ⊆ S" shows "NS⇧* O S ⊆ S"
using non_strict_into_strict [where S = S and NS = NS] assms by blast
lemma right_comp_S [simp]:
assumes "(x, y) ∈ S O (S O S⇧* O NS⇧* ∪ NS⇧*)"
shows "(x, y) ∈ (S O S⇧* O NS⇧*)"
proof-
from assms have "(x, y) ∈ (S O S O S⇧* O NS⇧*) ∪ (S O NS⇧*)" by auto
then have xy:"(x, y) ∈ (S O (S O S⇧*) O NS⇧*) ∪ (S O NS⇧*)" by auto
have "S O S⇧* ⊆ S⇧*" by auto
with xy have "(x, y) ∈ (S O S⇧* O NS⇧*) ∪ (S O NS⇧*)" by auto
then show "(x, y) ∈ (S O S⇧* O NS⇧*)" by auto
qed
lemma compatible_SN:
assumes SN: "SN S"
and compat: "NS O S ⊆ S"
shows "SN (S O S⇧* O NS⇧*)" (is "SN ?A")
proof
fix F assume chain: "chain ?A F"
from compat compat_tr_compat have tr_compat: "NS⇧* O S ⊆ S" by blast
have "∀i. (∃y z. (F i, y) ∈ S ∧ (y, z) ∈ S⇧* ∧ (z, F (Suc i)) ∈ NS⇧*)"
proof
fix i
from chain have "(F i, F (Suc i)) ∈ (S O S⇧* O NS⇧*)" by auto
then show "∃ y z. (F i, y) ∈ S ∧ (y, z) ∈ S⇧* ∧ (z, F (Suc i)) ∈ NS⇧*"
unfolding relcomp_def using mem_Collect_eq by auto
qed
then have "∃ f. (∀ i. (∃ z. (F i, f i) ∈ S ∧ ((f i, z) ∈ S⇧*) ∧(z, F (Suc i)) ∈ NS⇧*))"
by (rule choice)
then obtain f
where "∀ i. (∃ z. (F i, f i) ∈ S ∧ ((f i, z) ∈ S⇧*) ∧(z, F (Suc i)) ∈ NS⇧*)" ..
then have "∃ g. ∀ i. (F i, f i) ∈ S ∧ (f i, g i) ∈ S⇧* ∧ (g i, F (Suc i)) ∈ NS⇧*"
by (rule choice)
then obtain g where "∀ i. (F i, f i) ∈ S ∧ (f i, g i) ∈ S⇧* ∧ (g i, F (Suc i)) ∈ NS⇧*" ..
then have "∀ i. (f i, g i) ∈ S⇧* ∧ (g i, F (Suc i)) ∈ NS⇧* ∧ (F (Suc i), f (Suc i)) ∈ S"
by auto
then have "∀ i. (f i, g i) ∈ S⇧* ∧ (g i, f (Suc i)) ∈ S" unfolding relcomp_def
using tr_compat by auto
then have all:"∀ i. (f i, g i) ∈ S⇧* ∧ (g i, f (Suc i)) ∈ S⇧+" by auto
have "∀ i. (f i, f (Suc i)) ∈ S⇧+"
proof
fix i
from all have "(f i, g i) ∈ S⇧* ∧ (g i, f (Suc i)) ∈ S⇧+" ..
then show "(f i, f (Suc i)) ∈ S⇧+" using transitive_closure_trans by auto
qed
then have "∃x. f 0 = x ∧ chain (S⇧+) f"by auto
then obtain x where "f 0 = x ∧ chain (S⇧+) f" by auto
then have "∃f. f 0 = x ∧ chain (S⇧+) f" by auto
then have "¬ SN_on (S⇧+) {x}" by auto
then have "¬ SN (S⇧+)" unfolding SN_defs by auto
then have wfSconv:"¬ wf ((S⇧+)¯)" using SN_iff_wf by auto
from SN have "wf (S¯)" using SN_imp_wf [where?r=S] by simp
with wf_converse_trancl wfSconv show False by auto
qed
lemma compatible_rtrancl_split:
assumes compat: "NS O S ⊆ S"
and steps: "(x, y) ∈ (NS ∪ S)⇧*"
shows "(x, y) ∈ S O S⇧* O NS⇧* ∪ NS⇧*"
proof-
from steps have "∃ n. (x, y) ∈ (NS ∪ S)^^n" using rtrancl_imp_relpow [where ?R="NS ∪ S"] by auto
then obtain n where "(x, y) ∈ (NS ∪ S)^^n" by auto
then show "(x, y) ∈ S O S⇧* O NS⇧* ∪ NS⇧*"
proof (induct n arbitrary: x, simp)
case (Suc m)
assume "(x, y) ∈ (NS ∪ S)^^(Suc m)"
then have "∃ z. (x, z) ∈ (NS ∪ S) ∧ (z, y) ∈ (NS ∪ S)^^m"
using relpow_Suc_D2 [where ?R="NS ∪ S"] by auto
then obtain z where xz:"(x, z) ∈ (NS ∪ S)" and zy:"(z, y) ∈ (NS ∪ S)^^m" by auto
with Suc have zy:"(z, y) ∈ S O S⇧* O NS⇧* ∪ NS⇧*" by auto
then show "(x, y) ∈ S O S⇧* O NS⇧* ∪ NS⇧*"
proof (cases "(x, z) ∈ NS")
case True
from compat compat_tr_compat have trCompat: "NS⇧* O S ⊆ S" by blast
from zy True have "(x, y) ∈ (NS O S O S⇧* O NS⇧*) ∪ (NS O NS⇧*)" by auto
then have "(x, y) ∈ ((NS O S) O S⇧* O NS⇧*) ∪ (NS O NS⇧*)" by auto
then have "(x, y) ∈ ((NS⇧* O S) O S⇧* O NS⇧*) ∪ (NS O NS⇧*)" by auto
with trCompat have xy:"(x, y) ∈ (S O S⇧* O NS⇧*) ∪ (NS O NS⇧*)" by auto
have "NS O NS⇧* ⊆ NS⇧*" by auto
with xy show "(x, y) ∈ (S O S⇧* O NS⇧*) ∪ NS⇧*" by auto
next
case False
with xz have xz:"(x, z) ∈ S" by auto
with zy have "(x, y) ∈ S O (S O S⇧* O NS⇧* ∪ NS⇧*)" by auto
then show "(x, y) ∈ (S O S⇧* O NS⇧*) ∪ NS⇧*" using right_comp_S by simp
qed
qed
qed
lemma compatible_conv:
assumes compat: "NS O S ⊆ S"
shows "(NS ∪ S)⇧* O S O (NS ∪ S)⇧* = S O S⇧* O NS⇧*"
proof -
let ?NSuS = "NS ∪ S"
let ?NSS = "S O S⇧* O NS⇧*"
let ?midS = "?NSuS⇧* O S O ?NSuS⇧*"
have one: "?NSS ⊆ ?midS" by regexp
have "?NSuS⇧* O S ⊆ (?NSS ∪ NS⇧*) O S"
using compatible_rtrancl_split [where S = S and NS = NS] compat by blast
also have "… ⊆ ?NSS O S ∪ NS⇧* O S" by auto
also have "… ⊆ ?NSS O S ∪ S" using compat compat_tr_compat [where S = S and NS = NS] by auto
also have "… ⊆ S O ?NSuS⇧*" by regexp
finally have "?midS ⊆ S O ?NSuS⇧* O ?NSuS⇧*" by blast
also have "… ⊆ S O ?NSuS⇧*" by regexp
also have "… ⊆ S O (?NSS ∪ NS⇧*)"
using compatible_rtrancl_split [where S = S and NS = NS] compat by blast
also have "… ⊆ ?NSS" by regexp
finally have two: "?midS ⊆ ?NSS" .
from one two show ?thesis by auto
qed
lemma compatible_SN':
assumes compat: "NS O S ⊆ S" and SN: "SN S"
shows "SN((NS ∪ S)⇧* O S O (NS ∪ S)⇧*)"
using compatible_conv [where S = S and NS = NS]
compatible_SN [where S = S and NS = NS] assms by force
lemma rtrancl_diff_decomp:
assumes "(x, y) ∈ A⇧* - B⇧*"
shows "(x, y) ∈ A⇧* O (A - B) O A⇧*"
proof-
from assms have A: "(x, y) ∈ A⇧*" and B:"(x, y) ∉ B⇧*" by auto
from A have "∃ k. (x, y) ∈ A^^k" by (rule rtrancl_imp_relpow)
then obtain k where Ak:"(x, y) ∈ A^^k" by auto
from Ak B show "(x, y) ∈ A⇧* O (A - B) O A⇧*"
proof (induct k arbitrary: x)
case 0
with ‹(x, y) ∉ B⇧*› 0 show ?case using ccontr by auto
next
case (Suc i)
then have B:"(x, y) ∉ B⇧*" and ASk:"(x, y) ∈ A ^^ Suc i" by auto
from ASk have "∃z. (x, z) ∈ A ∧ (z, y) ∈ A ^^ i" using relpow_Suc_D2 [where ?R=A] by auto
then obtain z where xz:"(x, z) ∈ A" and "(z, y) ∈ A ^^ i" by auto
then have zy:"(z, y) ∈ A⇧*" using relpow_imp_rtrancl by auto
from xz show "(x, y) ∈ A⇧* O (A - B) O A⇧*"
proof (cases "(x, z) ∈ B")
case False
with xz zy show "(x, y) ∈ A⇧* O (A - B) O A⇧*" by auto
next
case True
then have "(x, z) ∈ B⇧*" by auto
have "⟦(x, z) ∈ B⇧*; (z, y) ∈ B⇧*⟧ ⟹ (x, y) ∈ B⇧*" using rtrancl_trans [of x z B] by auto
with ‹(x, z) ∈ B⇧*› ‹(x, y) ∉ B⇧*› have "(z, y) ∉ B⇧*" by auto
with Suc ‹(z, y) ∈ A ^^ i› have "(z, y) ∈ A⇧* O (A - B) O A⇧*" by auto
with xz have xy:"(x, y) ∈ A O A⇧* O (A - B) O A⇧*" by auto
have "A O A⇧* O (A - B) O A⇧* ⊆ A⇧* O (A - B) O A⇧*" by regexp
from this xy show "(x, y) ∈ A⇧* O (A - B) O A⇧*"
using subsetD [where ?A="A O A⇧* O (A - B) O A⇧*"] by auto
qed
qed
qed
lemma SN_empty [simp]: "SN {}" by auto
lemma SN_on_weakening:
assumes "SN_on R1 A"
shows "SN_on (R1 ∩ R2) A"
proof -
{
assume "∃S. S 0 ∈ A ∧ chain (R1 ∩ R2) S"
then obtain S where
S0: "S 0 ∈ A" and
SN: "chain (R1 ∩ R2) S"
by auto
from SN have SN': "chain R1 S" by simp
with S0 and assms have "False" by auto
}
then show ?thesis by force
qed
definition ideriv :: "'a rel ⇒ 'a rel ⇒ (nat ⇒ 'a) ⇒ bool" where
"ideriv R S as ⟷ (∀i. (as i, as (Suc i)) ∈ R ∪ S) ∧ (INFM i. (as i, as (Suc i)) ∈ R)"
lemma ideriv_mono: "R ⊆ R' ⟹ S ⊆ S' ⟹ ideriv R S as ⟹ ideriv R' S' as"
unfolding ideriv_def INFM_nat by blast
fun
shift :: "(nat ⇒ 'a) ⇒ nat ⇒ nat ⇒ 'a"
where
"shift f j = (λ i. f (i+j))"
lemma ideriv_split:
assumes ideriv: "ideriv R S as"
and nideriv: "¬ ideriv (D ∩ (R ∪ S)) (R ∪ S - D) as"
shows "∃ i. ideriv (R - D) (S - D) (shift as i)"
proof -
have RS: "R - D ∪ (S - D) = R ∪ S - D" by auto
from ideriv [unfolded ideriv_def]
have as: "⋀ i. (as i, as (Suc i)) ∈ R ∪ S"
and inf: "INFM i. (as i, as (Suc i)) ∈ R" by auto
show ?thesis
proof (cases "INFM i. (as i, as (Suc i)) ∈ D ∩ (R ∪ S)")
case True
have "ideriv (D ∩ (R ∪ S)) (R ∪ S - D) as"
unfolding ideriv_def
using as True by auto
with nideriv show ?thesis ..
next
case False
from False [unfolded INFM_nat]
obtain i where Dn: "⋀ j. i < j ⟹ (as j, as (Suc j)) ∉ D ∩ (R ∪ S)"
by auto
from Dn as have as: "⋀ j. i < j ⟹ (as j, as (Suc j)) ∈ R ∪ S - D" by auto
show ?thesis
proof (rule exI [of _ "Suc i"], unfold ideriv_def RS, insert as, intro conjI, simp, unfold INFM_nat, intro allI)
fix m
from inf [unfolded INFM_nat] obtain j where j: "j > Suc i + m"
and R: "(as j, as (Suc j)) ∈ R" by auto
with as [of j] have RD: "(as j, as (Suc j)) ∈ R - D" by auto
show "∃ j > m. (shift as (Suc i) j, shift as (Suc i) (Suc j)) ∈ R - D"
by (rule exI [of _ "j - Suc i"], insert j RD, auto)
qed
qed
qed
lemma ideriv_SN:
assumes SN: "SN S"
and compat: "NS O S ⊆ S"
and R: "R ⊆ NS ∪ S"
shows "¬ ideriv (S ∩ R) (R - S) as"
proof
assume "ideriv (S ∩ R) (R - S) as"
with R have steps: "∀ i. (as i, as (Suc i)) ∈ NS ∪ S"
and inf: "INFM i. (as i, as (Suc i)) ∈ S ∩ R" unfolding ideriv_def by auto
from non_strict_ending [OF steps compat] SN
obtain i where i: "⋀ j. j ≥ i ⟹ (as j, as (Suc j)) ∈ NS - S" by fast
from inf [unfolded INFM_nat] obtain j where "j > i" and "(as j, as (Suc j)) ∈ S" by auto
with i [of j] show False by auto
qed
lemma Infm_shift: "(INFM i. P (shift f n i)) = (INFM i. P (f i))" (is "?S = ?O")
proof
assume ?S
show ?O
unfolding INFM_nat_le
proof
fix m
from ‹?S› [unfolded INFM_nat_le]
obtain k where k: "k ≥ m" and p: "P (shift f n k)" by auto
show "∃ k ≥ m. P (f k)"
by (rule exI [of _ "k + n"], insert k p, auto)
qed
next
assume ?O
show ?S
unfolding INFM_nat_le
proof
fix m
from ‹?O› [unfolded INFM_nat_le]
obtain k where k: "k ≥ m + n" and p: "P (f k)" by auto
show "∃ k ≥ m. P (shift f n k)"
by (rule exI [of _ "k - n"], insert k p, auto)
qed
qed
lemma rtrancl_list_conv:
"(s, t) ∈ R⇧* ⟷
(∃ ts. last (s # ts) = t ∧ (∀i<length ts. ((s # ts) ! i, (s # ts) ! Suc i) ∈ R))" (is "?l = ?r")
proof
assume ?r
then obtain ts where "last (s # ts) = t ∧ (∀i<length ts. ((s # ts) ! i, (s # ts) ! Suc i) ∈ R)" ..
then show ?l
proof (induct ts arbitrary: s, simp)
case (Cons u ll)
then have "last (u # ll) = t ∧ (∀i<length ll. ((u # ll) ! i, (u # ll) ! Suc i) ∈ R)" by auto
from Cons(1)[OF this] have rec: "(u, t) ∈ R⇧*" .
from Cons have "(s, u) ∈ R" by auto
with rec show ?case by auto
qed
next
assume ?l
from rtrancl_imp_seq [OF this]
obtain S n where s: "S 0 = s" and t: "S n = t" and steps: "∀ i<n. (S i, S (Suc i)) ∈ R" by auto
let ?ts = "map (λ i. S (Suc i)) [0 ..< n]"
show ?r
proof (rule exI [of _ ?ts], intro conjI,
cases n, simp add: s [symmetric] t [symmetric], simp add: t [symmetric])
show "∀ i < length ?ts. ((s # ?ts) ! i, (s # ?ts) ! Suc i) ∈ R"
proof (intro allI impI)
fix i
assume i: "i < length ?ts"
then show "((s # ?ts) ! i, (s # ?ts) ! Suc i) ∈ R"
proof (cases i, simp add: s [symmetric] steps)
case (Suc j)
with i steps show ?thesis by simp
qed
qed
qed
qed
lemma SN_reaches_NF:
assumes "SN_on r {x}"
shows "∃y. (x, y) ∈ r⇧* ∧ y ∈ NF r"
using assms
proof (induct rule: SN_on_induct')
case (IH x)
show ?case
proof (cases "x ∈ NF r")
case True
then show ?thesis by auto
next
case False
then obtain y where step: "(x, y) ∈ r" by auto
from IH [OF this] obtain z where steps: "(y, z) ∈ r⇧*" and NF: "z ∈ NF r" by auto
show ?thesis
by (intro exI, rule conjI [OF _ NF], insert step steps, auto)
qed
qed
lemma SN_WCR_reaches_NF:
assumes SN: "SN_on r {x}"
and WCR: "WCR_on r {x. SN_on r {x}}"
shows "∃! y. (x, y) ∈ r⇧* ∧ y ∈ NF r"
proof -
from SN_reaches_NF [OF SN] obtain y where steps: "(x, y) ∈ r⇧*" and NF: "y ∈ NF r" by auto
show ?thesis
proof(rule, rule conjI [OF steps NF])
fix z
assume steps': "(x, z) ∈ r⇧* ∧ z ∈ NF r"
from Newman_local [OF SN WCR] have "CR_on r {x}" by auto
from CR_onD [OF this _ steps] steps' have "(y, z) ∈ r⇧↓" by simp
from join_NF_imp_eq [OF this NF] steps' show "z = y" by simp
qed
qed
definition some_NF :: "'a rel ⇒ 'a ⇒ 'a" where
"some_NF r x = (SOME y. (x, y) ∈ r⇧* ∧ y ∈ NF r)"
lemma some_NF:
assumes SN: "SN_on r {x}"
shows "(x, some_NF r x) ∈ r⇧* ∧ some_NF r x ∈ NF r"
using someI_ex [OF SN_reaches_NF [OF SN]]
unfolding some_NF_def .
lemma some_NF_WCR:
assumes SN: "SN_on r {x}"
and WCR: "WCR_on r {x. SN_on r {x}}"
and steps: "(x, y) ∈ r⇧*"
and NF: "y ∈ NF r"
shows "y = some_NF r x"
proof -
let ?p = "λ y. (x, y) ∈ r⇧* ∧ y ∈ NF r"
from SN_WCR_reaches_NF [OF SN WCR]
have one: "∃! y. ?p y" .
from steps NF have y: "?p y" ..
from some_NF [OF SN] have some: "?p (some_NF r x)" .
from one some y show ?thesis by auto
qed
lemma some_NF_UNF:
assumes UNF: "UNF r"
and steps: "(x, y) ∈ r⇧*"
and NF: "y ∈ NF r"
shows "y = some_NF r x"
proof -
let ?p = "λ y. (x, y) ∈ r⇧* ∧ y ∈ NF r"
from steps NF have py: "?p y" by simp
then have pNF: "?p (some_NF r x)" unfolding some_NF_def
by (rule someI)
from py have y: "(x, y) ∈ r⇧!" by auto
from pNF have nf: "(x, some_NF r x) ∈ r⇧!" by auto
from UNF [unfolded UNF_on_def] y nf show ?thesis by auto
qed
definition "the_NF A a = (THE b. (a, b) ∈ A⇧!)"
context
fixes A
assumes SN: "SN A" and CR: "CR A"
begin
lemma the_NF: "(a, the_NF A a) ∈ A⇧!"
proof -
obtain b where ab: "(a, b) ∈ A⇧!" using SN by (meson SN_imp_WN UNIV_I WN_onE)
moreover have "(a, c) ∈ A⇧! ⟹ c = b" for c
using CR and ab by (meson CR_divergence_imp_join join_NF_imp_eq normalizability_E)
ultimately have "∃!b. (a, b) ∈ A⇧!" by blast
then show ?thesis unfolding the_NF_def by (rule theI')
qed
lemma the_NF_NF: "the_NF A a ∈ NF A"
using the_NF by (auto simp: normalizability_def)
lemma the_NF_step:
assumes "(a, b) ∈ A"
shows "the_NF A a = the_NF A b"
using the_NF and assms
by (meson CR SN SN_imp_WN conversionI' r_into_rtrancl semi_complete_imp_conversionIff_same_NF semi_complete_onI)
lemma the_NF_steps:
assumes "(a, b) ∈ A⇧*"
shows "the_NF A a = the_NF A b"
using assms by (induct) (auto dest: the_NF_step)
lemma the_NF_conv:
assumes "(a, b) ∈ A⇧↔⇧*"
shows "the_NF A a = the_NF A b"
using assms
by (meson CR WN_on_def the_NF semi_complete_imp_conversionIff_same_NF semi_complete_onI)
end
definition weak_diamond :: "'a rel ⇒ bool" ("w◇") where
"w◇ r ⟷ (r¯ O r) - Id ⊆ (r O r¯)"
lemma weak_diamond_imp_CR:
assumes wd: "w◇ r"
shows "CR r"
proof (rule semi_confluence_imp_CR, rule)
fix x y
assume "(x, y) ∈ r¯ O r⇧*"
then obtain z where step: "(z, x) ∈ r" and steps: "(z, y) ∈ r⇧*" by auto
from steps
have "∃ u. (x, u) ∈ r⇧* ∧ (y, u) ∈ r⇧="
proof (induct)
case base
show ?case
by (rule exI [of _ x], insert step, auto)
next
case (step y' y)
from step(3) obtain u where xu: "(x, u) ∈ r⇧*" and y'u: "(y', u) ∈ r⇧=" by auto
from y'u have "(y', u) ∈ r ∨ y' = u" by auto
then show ?case
proof
assume y'u: "y' = u"
with xu step(2) have xy: "(x, y) ∈ r⇧*" by auto
show ?thesis
by (intro exI conjI, rule xy, simp)
next
assume "(y', u) ∈ r"
with step(2) have uy: "(u, y) ∈ r¯ O r" by auto
show ?thesis
proof (cases "u = y")
case True
show ?thesis
by (intro exI conjI, rule xu, unfold True, simp)
next
case False
with uy
wd [unfolded weak_diamond_def] obtain u' where uu': "(u, u') ∈ r"
and yu': "(y, u') ∈ r" by auto
from xu uu' have xu: "(x, u') ∈ r⇧*" by auto
show ?thesis
by (intro exI conjI, rule xu, insert yu', auto)
qed
qed
qed
then show "(x, y) ∈ r⇧↓" by auto
qed
lemma steps_imp_not_SN_on:
fixes t :: "'a ⇒ 'b"
and R :: "'b rel"
assumes steps: "⋀ x. (t x, t (f x)) ∈ R"
shows "¬ SN_on R {t x}"
proof
let ?U = "range t"
assume "SN_on R {t x}"
from SN_on_imp_on_minimal [OF this, rule_format, of ?U]
obtain tz where tz: "tz ∈ range t" and min: "⋀ y. (tz, y) ∈ R ⟹ y ∉ range t" by auto
from tz obtain z where tz: "tz = t z" by auto
from steps [of z] min [of "t (f z)"] show False unfolding tz by auto
qed
lemma steps_imp_not_SN:
fixes t :: "'a ⇒ 'b"
and R :: "'b rel"
assumes steps: "⋀ x. (t x, t (f x)) ∈ R"
shows "¬ SN R"
proof -
from steps_imp_not_SN_on [of t f R, OF steps]
show ?thesis unfolding SN_def by blast
qed
lemma steps_map:
assumes fg: "⋀t u R . P t ⟹ Q R ⟹ (t, u) ∈ R ⟹ P u ∧ (f t, f u) ∈ g R"
and t: "P t"
and R: "Q R"
and S: "Q S"
shows "((t, u) ∈ R⇧* ⟶ (f t, f u) ∈ (g R)⇧*)
∧ ((t, u) ∈ R⇧* O S O R⇧* ⟶ (f t, f u) ∈ (g R)⇧* O (g S) O (g R)⇧*)"
proof -
{
fix t u
assume "(t, u) ∈ R⇧*" and "P t"
then have "P u ∧ (f t, f u) ∈ (g R)⇧*"
proof (induct)
case (step u v)
from step(3)[OF step(4)] have Pu: "P u" and steps: "(f t, f u) ∈ (g R)⇧*" by auto
from fg [OF Pu R step(2)] have Pv: "P v" and step: "(f u, f v) ∈ g R" by auto
with steps have "(f t, f v) ∈ (g R)⇧*" by auto
with Pv show ?case by simp
qed simp
} note main = this
note maint = main [OF _ t]
from maint [of u] have one: "(t, u) ∈ R⇧* ⟶ (f t, f u) ∈ (g R)⇧*" by simp
show ?thesis
proof (rule conjI [OF one impI])
assume "(t, u) ∈ R⇧* O S O R⇧*"
then obtain s v where ts: "(t, s) ∈ R⇧*" and sv: "(s, v) ∈ S" and vu: "(v, u) ∈ R⇧*" by auto
from maint [OF ts] have Ps: "P s" and ts: "(f t, f s) ∈ (g R)⇧*" by auto
from fg [OF Ps S sv] have Pv: "P v" and sv: "(f s, f v) ∈ g S" by auto
from main [OF vu Pv] have vu: "(f v, f u) ∈ (g R)⇧*" by auto
from ts sv vu show "(f t, f u) ∈ (g R)⇧* O g S O (g R)⇧*" by auto
qed
qed
subsection ‹Terminating part of a relation›
inductive_set
SN_part :: "'a rel ⇒ 'a set"
for r :: "'a rel"
where
SN_partI: "(⋀y. (x, y) ∈ r ⟹ y ∈ SN_part r) ⟹ x ∈ SN_part r"
text ‹The accessible part of a relation is the same as the terminating part
(just two names for the same definition -- modulo argument order). See
@{thm accI}.›
text ‹Characterization of @{const SN_on} via terminating part.›
lemma SN_on_SN_part_conv:
"SN_on r A ⟷ A ⊆ SN_part r"
proof -
{
fix x assume "SN_on r A" and "x ∈ A"
then have "x ∈ SN_part r" by (induct) (auto intro: SN_partI)
} moreover {
fix x assume "x ∈ A" and "A ⊆ SN_part r"
then have "x ∈ SN_part r" by auto
then have "SN_on r {x}" by (induct) (auto intro: step_reflects_SN_on)
} ultimately show ?thesis by (force simp: SN_defs)
qed
text ‹Special case for ``full'' termination.›
lemma SN_SN_part_UNIV_conv:
"SN r ⟷ SN_part r = UNIV"
using SN_on_SN_part_conv [of r UNIV] by auto
lemma closed_imp_rtrancl_closed: assumes L: "L ⊆ A"
and R: "R `` A ⊆ A"
shows "{t | s. s ∈ L ∧ (s,t) ∈ R^*} ⊆ A"
proof -
{
fix s t
assume "(s,t) ∈ R^*" and "s ∈ L"
hence "t ∈ A"
by (induct, insert L R, auto)
}
thus ?thesis by auto
qed
lemma trancl_steps_relpow: assumes "a ⊆ b^+"
shows "(x,y) ∈ a^^n ⟹ ∃ m. m ≥ n ∧ (x,y) ∈ b^^m"
proof (induct n arbitrary: y)
case 0 thus ?case by (intro exI[of _ 0], auto)
next
case (Suc n z)
from Suc(2) obtain y where xy: "(x,y) ∈ a ^^ n" and yz: "(y,z) ∈ a" by auto
from Suc(1)[OF xy] obtain m where m: "m ≥ n" and xy: "(x,y) ∈ b ^^ m" by auto
from yz assms have "(y,z) ∈ b^+" by auto
from this[unfolded trancl_power] obtain k where k: "k > 0" and yz: "(y,z) ∈ b ^^ k" by auto
from xy yz have "(x,z) ∈ b ^^ (m + k)" unfolding relpow_add by auto
with k m show ?case by (intro exI[of _ "m + k"], auto)
qed
lemma relpow_image: assumes f: "⋀ s t. (s,t) ∈ r ⟹ (f s, f t) ∈ r'"
shows "(s,t) ∈ r ^^ n ⟹ (f s, f t) ∈ r' ^^ n"
proof (induct n arbitrary: t)
case (Suc n u)
from Suc(2) obtain t where st: "(s,t) ∈ r ^^ n" and tu: "(t,u) ∈ r" by auto
from Suc(1)[OF st] f[OF tu] show ?case by auto
qed auto
lemma relpow_refl_mono:
assumes refl:"⋀ x. (x,x) ∈ Rel"
shows "m ≤ n ⟹(a,b) ∈ Rel ^^ m ⟹ (a,b) ∈ Rel ^^ n"
proof (induct rule:dec_induct)
case (step i)
hence abi:"(a, b) ∈ Rel ^^ i" by auto
from refl[of b] abi relpowp_Suc_I[of i "λ x y. (x,y) ∈ Rel"] show "(a, b) ∈ Rel ^^ Suc i" by auto
qed
lemma SN_on_induct_acc_style [consumes 1, case_names IH]:
assumes sn: "SN_on R {a}"
and IH: "⋀x. SN_on R {x} ⟹ ⟦⋀y. (x, y) ∈ R ⟹ P y⟧ ⟹ P x"
shows "P a"
proof -
from sn SN_on_conv_acc [of "R¯" a] have a: "a ∈ termi R" by auto
show ?thesis
proof (rule Wellfounded.acc.induct [OF a, of P], rule IH)
fix x
assume "⋀y. (y, x) ∈ R¯ ⟹ y ∈ termi R"
from this [folded SN_on_conv_acc]
show "SN_on R {x}" by simp fast
qed auto
qed
lemma partially_localize_CR:
"CR r ⟷ (∀ x y z. (x, y) ∈ r ∧ (x, z) ∈ r⇧* ⟶ (y, z) ∈ join r)"
proof
assume "CR r"
thus "∀ x y z. (x, y) ∈ r ∧ (x, z) ∈ r⇧* ⟶ (y, z) ∈ join r" by auto
next
assume 1:"∀ x y z. (x, y) ∈ r ∧ (x, z) ∈ r⇧* ⟶ (y, z) ∈ join r"
show "CR r"
proof
fix a b c
assume 2: "a ∈ UNIV" and 3: "(a, b) ∈ r⇧*" and 4: "(a, c) ∈ r⇧*"
then obtain n where "(a,c) ∈ r^^n" using rtrancl_is_UN_relpow by fast
with 2 3 show "(b,c) ∈ join r"
proof (induct n arbitrary: a b c)
case 0 thus ?case by auto
next
case (Suc m)
from Suc(4) obtain d where ad: "(a, d) ∈ r^^m" and dc: "(d, c) ∈ r" by auto
from Suc(1) [OF Suc(2) Suc(3) ad] have "(b, d) ∈ join r" .
with 1 dc joinE joinI [of b _ r c] join_rtrancl_join show ?case by metis
qed
qed
qed
definition strongly_confluent_on :: "'a rel ⇒ 'a set ⇒ bool"
where
"strongly_confluent_on r A ⟷
(∀x ∈ A. ∀y z. (x, y) ∈ r ∧ (x, z) ∈ r ⟶ (∃u. (y, u) ∈ r⇧* ∧ (z, u) ∈ r⇧=))"
abbreviation strongly_confluent :: "'a rel ⇒ bool"
where
"strongly_confluent r ≡ strongly_confluent_on r UNIV"
lemma strongly_confluent_on_E11:
"strongly_confluent_on r A ⟹ x ∈ A ⟹ (x, y) ∈ r ⟹ (x, z) ∈ r ⟹
∃u. (y, u) ∈ r⇧* ∧ (z, u) ∈ r⇧="
unfolding strongly_confluent_on_def by blast
lemma strongly_confluentI [intro]:
"⟦⋀x y z. (x, y) ∈ r ⟹ (x, z) ∈ r ⟹ ∃u. (y, u) ∈ r⇧* ∧ (z, u) ∈ r⇧=⟧ ⟹ strongly_confluent r"
unfolding strongly_confluent_on_def by auto
lemma strongly_confluent_E1n:
assumes scr: "strongly_confluent r"
shows "(x, y) ∈ r⇧= ⟹ (x, z) ∈ r ^^ n ⟹ ∃u. (y, u) ∈ r⇧* ∧ (z, u) ∈ r⇧="
proof (induct n arbitrary: x y z)
case (Suc m)
from Suc(3) obtain w where xw: "(x, w) ∈ r^^m" and wz: "(w, z) ∈ r" by auto
from Suc(1) [OF Suc(2) xw] obtain u where yu: "(y, u) ∈ r⇧*" and wu: "(w, u) ∈ r⇧=" by auto
from strongly_confluent_on_E11 [OF scr, of w] wz yu wu show ?case
by (metis UnE converse_rtrancl_into_rtrancl iso_tuple_UNIV_I pair_in_Id_conv rtrancl_trans)
qed auto
lemma strong_confluence_imp_CR:
assumes "strongly_confluent r"
shows "CR r"
proof -
{ fix x y z
have "(x, y) ∈ r ⟹ (x, z) ∈ r⇧* ⟹ (y, z) ∈ join r"
by (cases "x = y", insert strongly_confluent_E1n [OF assms], blast+) }
then show "CR r" using partially_localize_CR by blast
qed
lemma WCR_alt_def: "WCR A ⟷ A¯ O A ⊆ A⇧↓" by (auto simp: WCR_defs)
lemma NF_imp_SN_on: "a ∈ NF R ⟹ SN_on R {a}" unfolding SN_on_def NF_def by blast
lemma Union_sym: "(s, t) ∈ (⋃i≤n. (S i)⇧↔) ⟷ (t, s) ∈ (⋃i≤n. (S i)⇧↔)" by auto
lemma peak_iff: "(x, y) ∈ A¯ O B ⟷ (∃u. (u, x) ∈ A ∧ (u, y) ∈ B)" by auto
lemma CR_NF_conv:
assumes "CR r" and "t ∈ NF r" and "(u, t) ∈ r⇧↔⇧*"
shows "(u, t) ∈ r⇧!"
using assms
unfolding CR_imp_conversionIff_join [OF ‹CR r›]
by (auto simp: NF_iff_no_step normalizability_def)
(metis (mono_tags) converse_rtranclE joinE)
lemma NF_join_imp_reach:
assumes "y ∈ NF A" and "(x, y) ∈ A⇧↓"
shows "(x, y) ∈ A⇧*"
using assms by (auto simp: join_def) (metis NF_not_suc rtrancl_converseD)
lemma conversion_O_conversion [simp]:
"A⇧↔⇧* O A⇧↔⇧* = A⇧↔⇧*"
by (force simp: converse_def)
lemma trans_O_iff: "trans A ⟷ A O A ⊆ A" unfolding trans_def by auto
lemma refl_O_iff: "refl A ⟷ Id ⊆ A" unfolding refl_on_def by auto
lemma relpow_Suc: "r ^^ Suc n = r O r ^^ n"
using relpow_add[of 1 n r] by auto
lemma converse_power: fixes r :: "'a rel" shows "(r¯)^^n = (r^^n)¯"
proof (induct n)
case (Suc n)
show ?case unfolding relpow.simps(2)[of _ "r¯"] relpow_Suc[of _ r]
by (simp add: Suc converse_relcomp)
qed simp
lemma conversion_mono: "A ⊆ B ⟹ A⇧↔⇧* ⊆ B⇧↔⇧*"
by (auto simp: conversion_def intro!: rtrancl_mono)
lemma conversion_conversion_idemp [simp]: "(A⇧↔⇧*)⇧↔⇧* = A⇧↔⇧*"
by auto
lemma lower_set_imp_not_SN_on:
assumes "s ∈ X" "∀t ∈ X. ∃u ∈ X. (t,u) ∈ R" shows "¬ SN_on R {s}"
by (meson SN_on_imp_on_minimal assms)
lemma SN_on_Image_rtrancl_iff[simp]: "SN_on R (R⇧* `` X) ⟷ SN_on R X" (is "?l = ?r")
proof(intro iffI)
assume "?l" show "?r" by (rule SN_on_subset2[OF _ ‹?l›], auto)
qed (fact SN_on_Image_rtrancl)
lemma O_mono1: "R ⊆ R' ⟹ S O R ⊆ S O R'" by auto
lemma O_mono2: "R ⊆ R' ⟹ R O T ⊆ R' O T" by auto
lemma rtrancl_O_shift: "(S O R)⇧* O S = S O (R O S)⇧*"
proof(intro equalityI subrelI)
fix x y
assume "(x,y) ∈ (S O R)⇧* O S"
then obtain n where "(x,y) ∈ (S O R)^^n O S" by blast
then show "(x,y) ∈ S O (R O S)⇧*"
proof(induct n arbitrary: y)
case IH: (Suc n)
then obtain z where xz: "(x,z) ∈ (S O R)^^n O S" and zy: "(z,y) ∈ R O S" by auto
from IH.hyps[OF xz] zy have "(x,y) ∈ S O (R O S)⇧* O R O S" by auto
then show ?case by(fold trancl_unfold_right, auto)
qed auto
next
fix x y
assume "(x,y) ∈ S O (R O S)⇧*"
then obtain n where "(x,y) ∈ S O (R O S)^^n" by blast
then show "(x,y) ∈ (S O R)⇧* O S"
proof(induct n arbitrary: y)
case IH: (Suc n)
then obtain z where xz: "(x,z) ∈ S O (R O S)^^n" and zy: "(z,y) ∈ R O S" by auto
from IH.hyps[OF xz] zy have "(x,y) ∈ ((S O R)⇧* O S O R) O S" by auto
from this[folded trancl_unfold_right]
show ?case by (rule rev_subsetD[OF _ O_mono2], auto simp: O_assoc)
qed auto
qed
lemma O_rtrancl_O_O: "R O (S O R)⇧* O S = (R O S)⇧+"
by (unfold rtrancl_O_shift trancl_unfold_left, auto)
lemma SN_on_subset_SN_terms:
assumes SN: "SN_on R X" shows "X ⊆ {x. SN_on R {x}}"
proof(intro subsetI, unfold mem_Collect_eq)
fix x assume x: "x ∈ X"
show "SN_on R {x}" by (rule SN_on_subset2[OF _ SN], insert x, auto)
qed
lemma SN_on_Un2:
assumes "SN_on R X" and "SN_on R Y" shows "SN_on R (X ∪ Y)"
using assms by fast
lemma SN_on_UN:
assumes "⋀x. SN_on R (X x)" shows "SN_on R (⋃x. X x)"
using assms by fast
lemma Image_subsetI: "R ⊆ R' ⟹ R `` X ⊆ R' `` X" by auto
lemma SN_on_O_comm:
assumes SN: "SN_on ((R :: ('a×'b) set) O (S :: ('b×'a) set)) (S `` X)"
shows "SN_on (S O R) X"
proof
fix seq :: "nat ⇒ 'b" assume seq0: "seq 0 ∈ X" and chain: "chain (S O R) seq"
from SN have SN: "SN_on (R O S) ((R O S)⇧* `` S `` X)" by simp
{ fix i a
assume ia: "(seq i,a) ∈ S" and aSi: "(a,seq (Suc i)) ∈ R"
have "seq i ∈ (S O R)⇧* `` X"
proof (induct i)
case 0 from seq0 show ?case by auto
next
case (Suc i) with chain have "seq (Suc i) ∈ ((S O R)⇧* O S O R) `` X" by blast
also have "... ⊆ (S O R)⇧* `` X" by (fold trancl_unfold_right, auto)
finally show ?case.
qed
with ia have "a ∈ ((S O R)⇧* O S) `` X" by auto
then have a: "a ∈ ((R O S)⇧*) `` S `` X" by (auto simp: rtrancl_O_shift)
with ia aSi have False
proof(induct "a" arbitrary: i rule: SN_on_induct[OF SN])
case 1 show ?case by (fact a)
next
case IH: (2 a)
from chain obtain b
where *: "(seq (Suc i), b) ∈ S" "(b, seq (Suc (Suc i))) ∈ R" by auto
with IH have ab: "(a,b) ∈ R O S" by auto
with ‹a ∈ (R O S)⇧* `` S `` X› have "b ∈ ((R O S)⇧* O R O S) `` S `` X" by auto
then have "b ∈ (R O S)⇧* `` S `` X"
by (rule rev_subsetD, intro Image_subsetI, fold trancl_unfold_right, auto)
from IH.hyps[OF ab * this] IH.prems ab show False by auto
qed
}
with chain show False by auto
qed
lemma SN_O_comm: "SN (R O S) ⟷ SN (S O R)"
by (intro iffI; rule SN_on_O_comm[OF SN_on_subset2], auto)
lemma chain_mono: assumes "R' ⊆ R" "chain R' seq" shows "chain R seq"
using assms by auto
context
fixes S R
assumes push: "S O R ⊆ R O S⇧*"
begin
lemma rtrancl_O_push: "S⇧* O R ⊆ R O S⇧*"
proof-
{ fix n
have "⋀s t. (s,t) ∈ S ^^ n O R ⟹ (s,t) ∈ R O S⇧*"
proof(induct n)
case (Suc n)
then obtain u where "(s,u) ∈ S" "(u,t) ∈ R O S⇧*" unfolding relpow_Suc by blast
then have "(s,t) ∈ S O R O S⇧*" by auto
also have "... ⊆ R O S⇧* O S⇧*" using push by blast
also have "... ⊆ R O S⇧*" by auto
finally show ?case.
qed auto
}
thus ?thesis by blast
qed
lemma rtrancl_U_push: "(S ∪ R)⇧* = R⇧* O S⇧*"
proof(intro equalityI subrelI)
fix x y
assume "(x,y) ∈ (S ∪ R)⇧*"
also have "... ⊆ (S⇧* O R)⇧* O S⇧*" by regexp
finally obtain z where xz: "(x,z) ∈ (S⇧* O R)⇧*" and zy: "(z,y) ∈ S⇧*" by auto
from xz have "(x,z) ∈ R⇧* O S⇧*"
proof (induct rule: rtrancl_induct)
case (step z w)
then have "(x,w) ∈ R⇧* O S⇧* O S⇧* O R" by auto
also have "... ⊆ R⇧* O S⇧* O R" by regexp
also have "... ⊆ R⇧* O R O S⇧*" using rtrancl_O_push by auto
also have "... ⊆ R⇧* O S⇧*" by regexp
finally show ?case.
qed auto
with zy show "(x,y) ∈ R⇧* O S⇧*" by auto
qed regexp
lemma SN_on_O_push:
assumes SN: "SN_on R X" shows "SN_on (R O S⇧*) X"
proof
fix seq
have SN: "SN_on R (R⇧* `` X)" using SN_on_Image_rtrancl[OF SN].
moreover assume "seq (0::nat) ∈ X"
then have "seq 0 ∈ R⇧* `` X" by auto
ultimately show "chain (R O S⇧*) seq ⟹ False"
proof(induct "seq 0" arbitrary: seq rule: SN_on_induct)
case IH
then have 01: "(seq 0, seq 1) ∈ R O S⇧*"
and 12: "(seq 1, seq 2) ∈ R O S⇧*"
and 23: "(seq 2, seq 3) ∈ R O S⇧*" by (auto simp: eval_nat_numeral)
then obtain s t
where s: "(seq 0, s) ∈ R" and s1: "(s, seq 1) ∈ S⇧*"
and t: "(seq 1, t) ∈ R" and t2: "(t, seq 2) ∈ S⇧*" by auto
from s1 t have "(s,t) ∈ S⇧* O R" by auto
with rtrancl_O_push have st: "(s,t) ∈ R O S⇧*" by auto
from t2 23 have "(t, seq 3) ∈ S⇧* O R O S⇧*" by auto
also from rtrancl_O_push have "... ⊆ R O S⇧* O S⇧*" by blast
finally have t3: "(t, seq 3) ∈ R O S⇧*" by regexp
let ?seq = "λi. case i of 0 ⇒ s | Suc 0 ⇒ t | i ⇒ seq (Suc i)"
show ?case
proof(rule IH)
from s show "(seq 0, ?seq 0) ∈ R" by auto
show "chain (R O S⇧*) ?seq"
proof (intro allI)
fix i show "(?seq i, ?seq (Suc i)) ∈ R O S⇧*"
proof (cases i)
case 0 with st show ?thesis by auto
next
case (Suc i) with t3 IH show ?thesis by (cases i, auto simp: eval_nat_numeral)
qed
qed
qed
qed
qed
lemma SN_on_Image_push:
assumes SN: "SN_on R X" shows "SN_on R (S⇧* `` X)"
proof-
{ fix n
have "SN_on R ((S^^n) `` X)"
proof(induct n)
case 0 from SN show ?case by auto
case (Suc n)
from SN_on_O_push[OF this] have "SN_on (R O S⇧*) ((S ^^ n) `` X)".
from SN_on_Image[OF this]
have "SN_on (R O S⇧*) ((R O S⇧*) `` (S ^^ n) `` X)".
then have "SN_on R ((R O S⇧*) `` (S ^^ n) `` X)" by (rule SN_on_mono, auto)
from SN_on_subset2[OF Image_mono[OF push subset_refl] this]
have "SN_on R (R `` (S ^^ Suc n) `` X)" by (auto simp: relcomp_Image)
then show ?case by fast
qed
}
then show ?thesis by fast
qed
end
lemma not_SN_onI[intro]: "f 0 ∈ X ⟹ chain R f ⟹ ¬ SN_on R X"
by (unfold SN_on_def not_not, intro exI conjI)
lemma shift_comp[simp]: "shift (f ∘ seq) n = f ∘ (shift seq n)" by auto
lemma Id_on_union: "Id_on (A ∪ B) = Id_on A ∪ Id_on B" unfolding Id_on_def by auto
lemma relpow_union_cases: "(a,d) ∈ (A ∪ B)^^n ⟹ (a,d) ∈ B^^n ∨ (∃ b c k m. (a,b) ∈ B^^k ∧ (b,c) ∈ A ∧ (c,d) ∈ (A ∪ B)^^m ∧ n = Suc (k + m))"
proof (induct n arbitrary: a d)
case (Suc n a e)
let ?AB = "A ∪ B"
from Suc(2) obtain b where ab: "(a,b) ∈ ?AB" and be: "(b,e) ∈ ?AB^^n" by (rule relpow_Suc_E2)
from ab
show ?case
proof
assume "(a,b) ∈ A"
show ?thesis
proof (rule disjI2, intro exI conjI)
show "Suc n = Suc (0 + n)" by simp
show "(a,b) ∈ A" by fact
qed (insert be, auto)
next
assume ab: "(a,b) ∈ B"
from Suc(1)[OF be]
show ?thesis
proof
assume "(b,e) ∈ B ^^ n"
with ab show ?thesis
by (intro disjI1 relpow_Suc_I2)
next
assume "∃ c d k m. (b, c) ∈ B ^^ k ∧ (c, d) ∈ A ∧ (d, e) ∈ ?AB ^^ m ∧ n = Suc (k + m)"
then obtain c d k m where "(b, c) ∈ B ^^ k" and *: "(c, d) ∈ A" "(d, e) ∈ ?AB ^^ m" "n = Suc (k + m)" by blast
with ab have ac: "(a,c) ∈ B ^^ (Suc k)" by (intro relpow_Suc_I2)
show ?thesis
by (intro disjI2 exI conjI, rule ac, (rule *)+, simp add: *)
qed
qed
qed simp
lemma trans_refl_imp_rtrancl_id:
assumes "trans r" "refl r"
shows "r⇧* = r"
proof
show "r⇧* ⊆ r"
proof
fix x y
assume "(x,y) ∈ r⇧*"
thus "(x,y) ∈ r"
by (induct, insert assms, unfold refl_on_def trans_def, blast+)
qed
qed regexp
lemma trans_refl_imp_O_id:
assumes "trans r" "refl r"
shows "r O r = r"
proof(intro equalityI)
show "r O r ⊆ r" by(fact trans_O_subset[OF assms(1)])
have "r ⊆ r O Id" by auto
moreover have "Id ⊆ r" by(fact assms(2)[unfolded refl_O_iff])
ultimately show "r ⊆ r O r" by auto
qed
lemma relcomp3_I:
assumes "(t, u) ∈ A" and "(s, t) ∈ B" and "(u, v) ∈ B"
shows "(s, v) ∈ B O A O B"
using assms by blast
lemma relcomp3_transI:
assumes "trans B" and "(t, u) ∈ B O A O B" and "(s, t) ∈ B" and "(u, v) ∈ B"
shows "(s, v) ∈ B O A O B"
using assms by (auto simp: trans_def intro: relcomp3_I)
lemmas converse_inward = rtrancl_converse[symmetric] converse_Un converse_UNION converse_relcomp
converse_converse converse_Id
lemma qc_SN_relto_iff:
assumes "r O s ⊆ s O (s ∪ r)⇧*"
shows "SN (r⇧* O s O r⇧*) = SN s"
proof -
from converse_mono [THEN iffD2 , OF assms]
have *: "s¯ O r¯ ⊆ (s¯ ∪ r¯)⇧* O s¯" unfolding converse_inward .
have "(r⇧* O s O r⇧*)¯ = (r¯)⇧* O s¯ O (r¯)⇧*"
by (simp only: converse_relcomp O_assoc rtrancl_converse)
with qc_wf_relto_iff [OF *]
show ?thesis by (simp add: SN_iff_wf)
qed
lemma conversion_empty [simp]: "conversion {} = Id"
by (auto simp: conversion_def)
lemma symcl_idemp [simp]: "(r⇧↔)⇧↔ = r⇧↔" by auto
end