header {* Partial orders *}
theory Porder
imports Main
begin
subsection {* Type class for partial orders *}
class below =
fixes below :: "'a => 'a => bool"
begin
notation
below (infix "<<" 50)
notation (xsymbols)
below (infix "\<sqsubseteq>" 50)
abbreviation
not_below :: "'a => 'a => bool" (infix "~<<" 50)
where "not_below x y ≡ ¬ below x y"
notation (xsymbols)
not_below (infix "\<notsqsubseteq>" 50)
lemma below_eq_trans: "[|a \<sqsubseteq> b; b = c|] ==> a \<sqsubseteq> c"
by (rule subst)
lemma eq_below_trans: "[|a = b; b \<sqsubseteq> c|] ==> a \<sqsubseteq> c"
by (rule ssubst)
end
class po = below +
assumes below_refl [iff]: "x \<sqsubseteq> x"
assumes below_trans: "x \<sqsubseteq> y ==> y \<sqsubseteq> z ==> x \<sqsubseteq> z"
assumes below_antisym: "x \<sqsubseteq> y ==> y \<sqsubseteq> x ==> x = y"
begin
lemma eq_imp_below: "x = y ==> x \<sqsubseteq> y"
by simp
lemma box_below: "a \<sqsubseteq> b ==> c \<sqsubseteq> a ==> b \<sqsubseteq> d ==> c \<sqsubseteq> d"
by (rule below_trans [OF below_trans])
lemma po_eq_conv: "x = y <-> x \<sqsubseteq> y ∧ y \<sqsubseteq> x"
by (fast intro!: below_antisym)
lemma rev_below_trans: "y \<sqsubseteq> z ==> x \<sqsubseteq> y ==> x \<sqsubseteq> z"
by (rule below_trans)
lemma not_below2not_eq: "x \<notsqsubseteq> y ==> x ≠ y"
by auto
end
lemmas HOLCF_trans_rules [trans] =
below_trans
below_antisym
below_eq_trans
eq_below_trans
context po
begin
subsection {* Upper bounds *}
definition is_ub :: "'a set => 'a => bool" (infix "<|" 55) where
"S <| x <-> (∀y∈S. y \<sqsubseteq> x)"
lemma is_ubI: "(!!x. x ∈ S ==> x \<sqsubseteq> u) ==> S <| u"
by (simp add: is_ub_def)
lemma is_ubD: "[|S <| u; x ∈ S|] ==> x \<sqsubseteq> u"
by (simp add: is_ub_def)
lemma ub_imageI: "(!!x. x ∈ S ==> f x \<sqsubseteq> u) ==> (λx. f x) ` S <| u"
unfolding is_ub_def by fast
lemma ub_imageD: "[|f ` S <| u; x ∈ S|] ==> f x \<sqsubseteq> u"
unfolding is_ub_def by fast
lemma ub_rangeI: "(!!i. S i \<sqsubseteq> x) ==> range S <| x"
unfolding is_ub_def by fast
lemma ub_rangeD: "range S <| x ==> S i \<sqsubseteq> x"
unfolding is_ub_def by fast
lemma is_ub_empty [simp]: "{} <| u"
unfolding is_ub_def by fast
lemma is_ub_insert [simp]: "(insert x A) <| y = (x \<sqsubseteq> y ∧ A <| y)"
unfolding is_ub_def by fast
lemma is_ub_upward: "[|S <| x; x \<sqsubseteq> y|] ==> S <| y"
unfolding is_ub_def by (fast intro: below_trans)
subsection {* Least upper bounds *}
definition is_lub :: "'a set => 'a => bool" (infix "<<|" 55) where
"S <<| x <-> S <| x ∧ (∀u. S <| u --> x \<sqsubseteq> u)"
definition lub :: "'a set => 'a" where
"lub S = (THE x. S <<| x)"
end
syntax
"_BLub" :: "[pttrn, 'a set, 'b] => 'b" ("(3LUB _:_./ _)" [0,0, 10] 10)
syntax (xsymbols)
"_BLub" :: "[pttrn, 'a set, 'b] => 'b" ("(3\<Squnion>_∈_./ _)" [0,0, 10] 10)
translations
"LUB x:A. t" == "CONST lub ((%x. t) ` A)"
context po
begin
abbreviation
Lub (binder "LUB " 10) where
"LUB n. t n == lub (range t)"
notation (xsymbols)
Lub (binder "\<Squnion> " 10)
text {* access to some definition as inference rule *}
lemma is_lubD1: "S <<| x ==> S <| x"
unfolding is_lub_def by fast
lemma is_lubD2: "[|S <<| x; S <| u|] ==> x \<sqsubseteq> u"
unfolding is_lub_def by fast
lemma is_lubI: "[|S <| x; !!u. S <| u ==> x \<sqsubseteq> u|] ==> S <<| x"
unfolding is_lub_def by fast
lemma is_lub_below_iff: "S <<| x ==> x \<sqsubseteq> u <-> S <| u"
unfolding is_lub_def is_ub_def by (metis below_trans)
text {* lubs are unique *}
lemma is_lub_unique: "[|S <<| x; S <<| y|] ==> x = y"
unfolding is_lub_def is_ub_def by (blast intro: below_antisym)
text {* technical lemmas about @{term lub} and @{term is_lub} *}
lemma is_lub_lub: "M <<| x ==> M <<| lub M"
unfolding lub_def by (rule theI [OF _ is_lub_unique])
lemma lub_eqI: "M <<| l ==> lub M = l"
by (rule is_lub_unique [OF is_lub_lub])
lemma is_lub_singleton: "{x} <<| x"
by (simp add: is_lub_def)
lemma lub_singleton [simp]: "lub {x} = x"
by (rule is_lub_singleton [THEN lub_eqI])
lemma is_lub_bin: "x \<sqsubseteq> y ==> {x, y} <<| y"
by (simp add: is_lub_def)
lemma lub_bin: "x \<sqsubseteq> y ==> lub {x, y} = y"
by (rule is_lub_bin [THEN lub_eqI])
lemma is_lub_maximal: "[|S <| x; x ∈ S|] ==> S <<| x"
by (erule is_lubI, erule (1) is_ubD)
lemma lub_maximal: "[|S <| x; x ∈ S|] ==> lub S = x"
by (rule is_lub_maximal [THEN lub_eqI])
subsection {* Countable chains *}
definition chain :: "(nat => 'a) => bool" where
-- {* Here we use countable chains and I prefer to code them as functions! *}
"chain Y = (∀i. Y i \<sqsubseteq> Y (Suc i))"
lemma chainI: "(!!i. Y i \<sqsubseteq> Y (Suc i)) ==> chain Y"
unfolding chain_def by fast
lemma chainE: "chain Y ==> Y i \<sqsubseteq> Y (Suc i)"
unfolding chain_def by fast
text {* chains are monotone functions *}
lemma chain_mono_less: "[|chain Y; i < j|] ==> Y i \<sqsubseteq> Y j"
by (erule less_Suc_induct, erule chainE, erule below_trans)
lemma chain_mono: "[|chain Y; i ≤ j|] ==> Y i \<sqsubseteq> Y j"
by (cases "i = j", simp, simp add: chain_mono_less)
lemma chain_shift: "chain Y ==> chain (λi. Y (i + j))"
by (rule chainI, simp, erule chainE)
text {* technical lemmas about (least) upper bounds of chains *}
lemma is_lub_rangeD1: "range S <<| x ==> S i \<sqsubseteq> x"
by (rule is_lubD1 [THEN ub_rangeD])
lemma is_ub_range_shift:
"chain S ==> range (λi. S (i + j)) <| x = range S <| x"
apply (rule iffI)
apply (rule ub_rangeI)
apply (rule_tac y="S (i + j)" in below_trans)
apply (erule chain_mono)
apply (rule le_add1)
apply (erule ub_rangeD)
apply (rule ub_rangeI)
apply (erule ub_rangeD)
done
lemma is_lub_range_shift:
"chain S ==> range (λi. S (i + j)) <<| x = range S <<| x"
by (simp add: is_lub_def is_ub_range_shift)
text {* the lub of a constant chain is the constant *}
lemma chain_const [simp]: "chain (λi. c)"
by (simp add: chainI)
lemma is_lub_const: "range (λx. c) <<| c"
by (blast dest: ub_rangeD intro: is_lubI ub_rangeI)
lemma lub_const [simp]: "(\<Squnion>i. c) = c"
by (rule is_lub_const [THEN lub_eqI])
subsection {* Finite chains *}
definition max_in_chain :: "nat => (nat => 'a) => bool" where
-- {* finite chains, needed for monotony of continuous functions *}
"max_in_chain i C <-> (∀j. i ≤ j --> C i = C j)"
definition finite_chain :: "(nat => 'a) => bool" where
"finite_chain C = (chain C ∧ (∃i. max_in_chain i C))"
text {* results about finite chains *}
lemma max_in_chainI: "(!!j. i ≤ j ==> Y i = Y j) ==> max_in_chain i Y"
unfolding max_in_chain_def by fast
lemma max_in_chainD: "[|max_in_chain i Y; i ≤ j|] ==> Y i = Y j"
unfolding max_in_chain_def by fast
lemma finite_chainI:
"[|chain C; max_in_chain i C|] ==> finite_chain C"
unfolding finite_chain_def by fast
lemma finite_chainE:
"[|finite_chain C; !!i. [|chain C; max_in_chain i C|] ==> R|] ==> R"
unfolding finite_chain_def by fast
lemma lub_finch1: "[|chain C; max_in_chain i C|] ==> range C <<| C i"
apply (rule is_lubI)
apply (rule ub_rangeI, rename_tac j)
apply (rule_tac x=i and y=j in linorder_le_cases)
apply (drule (1) max_in_chainD, simp)
apply (erule (1) chain_mono)
apply (erule ub_rangeD)
done
lemma lub_finch2:
"finite_chain C ==> range C <<| C (LEAST i. max_in_chain i C)"
apply (erule finite_chainE)
apply (erule LeastI2 [where Q="λi. range C <<| C i"])
apply (erule (1) lub_finch1)
done
lemma finch_imp_finite_range: "finite_chain Y ==> finite (range Y)"
apply (erule finite_chainE)
apply (rule_tac B="Y ` {..i}" in finite_subset)
apply (rule subsetI)
apply (erule rangeE, rename_tac j)
apply (rule_tac x=i and y=j in linorder_le_cases)
apply (subgoal_tac "Y j = Y i", simp)
apply (simp add: max_in_chain_def)
apply simp
apply simp
done
lemma finite_range_has_max:
fixes f :: "nat => 'a" and r :: "'a => 'a => bool"
assumes mono: "!!i j. i ≤ j ==> r (f i) (f j)"
assumes finite_range: "finite (range f)"
shows "∃k. ∀i. r (f i) (f k)"
proof (intro exI allI)
fix i :: nat
let ?j = "LEAST k. f k = f i"
let ?k = "Max ((λx. LEAST k. f k = x) ` range f)"
have "?j ≤ ?k"
proof (rule Max_ge)
show "finite ((λx. LEAST k. f k = x) ` range f)"
using finite_range by (rule finite_imageI)
show "?j ∈ (λx. LEAST k. f k = x) ` range f"
by (intro imageI rangeI)
qed
hence "r (f ?j) (f ?k)"
by (rule mono)
also have "f ?j = f i"
by (rule LeastI, rule refl)
finally show "r (f i) (f ?k)" .
qed
lemma finite_range_imp_finch:
"[|chain Y; finite (range Y)|] ==> finite_chain Y"
apply (subgoal_tac "∃k. ∀i. Y i \<sqsubseteq> Y k")
apply (erule exE)
apply (rule finite_chainI, assumption)
apply (rule max_in_chainI)
apply (rule below_antisym)
apply (erule (1) chain_mono)
apply (erule spec)
apply (rule finite_range_has_max)
apply (erule (1) chain_mono)
apply assumption
done
lemma bin_chain: "x \<sqsubseteq> y ==> chain (λi. if i=0 then x else y)"
by (rule chainI, simp)
lemma bin_chainmax:
"x \<sqsubseteq> y ==> max_in_chain (Suc 0) (λi. if i=0 then x else y)"
unfolding max_in_chain_def by simp
lemma is_lub_bin_chain:
"x \<sqsubseteq> y ==> range (λi::nat. if i=0 then x else y) <<| y"
apply (frule bin_chain)
apply (drule bin_chainmax)
apply (drule (1) lub_finch1)
apply simp
done
text {* the maximal element in a chain is its lub *}
lemma lub_chain_maxelem: "[|Y i = c; ∀i. Y i \<sqsubseteq> c|] ==> lub (range Y) = c"
by (blast dest: ub_rangeD intro: lub_eqI is_lubI ub_rangeI)
end
end