(* Title: HOL/BNF_Wellorder_Relation.thy
Author: Andrei Popescu, TU Muenchen
Copyright 2012
Well-order relations (BNF).
*)
header {* Well-Order Relations (BNF) *}
theory BNF_Wellorder_Relation
imports Order_Relation
begin
text{* In this section, we develop basic concepts and results pertaining
to well-order relations. Note that we consider well-order relations
as {\em non-strict relations},
i.e., as containing the diagonals of their fields. *}
locale wo_rel =
fixes r :: "'a rel"
assumes WELL: "Well_order r"
begin
text{* The following context encompasses all this section. In other words,
for the whole section, we consider a fixed well-order relation @{term "r"}. *}
(* context wo_rel *)
abbreviation under where "under \ Order_Relation.under r"
abbreviation underS where "underS \ Order_Relation.underS r"
abbreviation Under where "Under \ Order_Relation.Under r"
abbreviation UnderS where "UnderS \ Order_Relation.UnderS r"
abbreviation above where "above \ Order_Relation.above r"
abbreviation aboveS where "aboveS \ Order_Relation.aboveS r"
abbreviation Above where "Above \ Order_Relation.Above r"
abbreviation AboveS where "AboveS \ Order_Relation.AboveS r"
subsection {* Auxiliaries *}
lemma REFL: "Refl r"
using WELL order_on_defs[of _ r] by auto
lemma TRANS: "trans r"
using WELL order_on_defs[of _ r] by auto
lemma ANTISYM: "antisym r"
using WELL order_on_defs[of _ r] by auto
lemma TOTAL: "Total r"
using WELL order_on_defs[of _ r] by auto
lemma TOTALS: "\a \ Field r. \b \ Field r. (a,b) \ r \ (b,a) \ r"
using REFL TOTAL refl_on_def[of _ r] total_on_def[of _ r] by force
lemma LIN: "Linear_order r"
using WELL well_order_on_def[of _ r] by auto
lemma WF: "wf (r - Id)"
using WELL well_order_on_def[of _ r] by auto
lemma cases_Total:
"\ phi a b. \{a,b} <= Field r; ((a,b) \ r \ phi a b); ((b,a) \ r \ phi a b)\
\ phi a b"
using TOTALS by auto
lemma cases_Total3:
"\ phi a b. \{a,b} \ Field r; ((a,b) \ r - Id \ (b,a) \ r - Id \ phi a b);
(a = b \ phi a b)\ \ phi a b"
using TOTALS by auto
subsection {* Well-founded induction and recursion adapted to non-strict well-order relations *}
text{* Here we provide induction and recursion principles specific to {\em non-strict}
well-order relations.
Although minor variations of those for well-founded relations, they will be useful
for doing away with the tediousness of
having to take out the diagonal each time in order to switch to a well-founded relation. *}
lemma well_order_induct:
assumes IND: "\x. \y. y \ x \ (y, x) \ r \ P y \ P x"
shows "P a"
proof-
have "\x. \y. (y, x) \ r - Id \ P y \ P x"
using IND by blast
thus "P a" using WF wf_induct[of "r - Id" P a] by blast
qed
definition
worec :: "(('a \ 'b) \ 'a \ 'b) \ 'a \ 'b"
where
"worec F \ wfrec (r - Id) F"
definition
adm_wo :: "(('a \ 'b) \ 'a \ 'b) \ bool"
where
"adm_wo H \ \f g x. (\y \ underS x. f y = g y) \ H f x = H g x"
lemma worec_fixpoint:
assumes ADM: "adm_wo H"
shows "worec H = H (worec H)"
proof-
let ?rS = "r - Id"
have "adm_wf (r - Id) H"
unfolding adm_wf_def
using ADM adm_wo_def[of H] underS_def[of r] by auto
hence "wfrec ?rS H = H (wfrec ?rS H)"
using WF wfrec_fixpoint[of ?rS H] by simp
thus ?thesis unfolding worec_def .
qed
subsection {* The notions of maximum, minimum, supremum, successor and order filter *}
text{*
We define the successor {\em of a set}, and not of an element (the latter is of course
a particular case). Also, we define the maximum {\em of two elements}, @{text "max2"},
and the minimum {\em of a set}, @{text "minim"} -- we chose these variants since we
consider them the most useful for well-orders. The minimum is defined in terms of the
auxiliary relational operator @{text "isMinim"}. Then, supremum and successor are
defined in terms of minimum as expected.
The minimum is only meaningful for non-empty sets, and the successor is only
meaningful for sets for which strict upper bounds exist.
Order filters for well-orders are also known as ``initial segments". *}
definition max2 :: "'a \ 'a \ 'a"
where "max2 a b \ if (a,b) \ r then b else a"
definition isMinim :: "'a set \ 'a \ bool"
where "isMinim A b \ b \ A \ (\a \ A. (b,a) \ r)"
definition minim :: "'a set \ 'a"
where "minim A \ THE b. isMinim A b"
definition supr :: "'a set \ 'a"
where "supr A \ minim (Above A)"
definition suc :: "'a set \ 'a"
where "suc A \ minim (AboveS A)"
definition ofilter :: "'a set \ bool"
where
"ofilter A \ (A \ Field r) \ (\a \ A. under a \ A)"
subsubsection {* Properties of max2 *}
lemma max2_greater_among:
assumes "a \ Field r" and "b \ Field r"
shows "(a, max2 a b) \ r \ (b, max2 a b) \ r \ max2 a b \ {a,b}"
proof-
{assume "(a,b) \ r"
hence ?thesis using max2_def assms REFL refl_on_def
by (auto simp add: refl_on_def)
}
moreover
{assume "a = b"
hence "(a,b) \ r" using REFL assms
by (auto simp add: refl_on_def)
}
moreover
{assume *: "a \ b \ (b,a) \ r"
hence "(a,b) \ r" using ANTISYM
by (auto simp add: antisym_def)
hence ?thesis using * max2_def assms REFL refl_on_def
by (auto simp add: refl_on_def)
}
ultimately show ?thesis using assms TOTAL
total_on_def[of "Field r" r] by blast
qed
lemma max2_greater:
assumes "a \ Field r" and "b \ Field r"
shows "(a, max2 a b) \ r \ (b, max2 a b) \ r"
using assms by (auto simp add: max2_greater_among)
lemma max2_among:
assumes "a \ Field r" and "b \ Field r"
shows "max2 a b \ {a, b}"
using assms max2_greater_among[of a b] by simp
lemma max2_equals1:
assumes "a \ Field r" and "b \ Field r"
shows "(max2 a b = a) = ((b,a) \ r)"
using assms ANTISYM unfolding antisym_def using TOTALS
by(auto simp add: max2_def max2_among)
lemma max2_equals2:
assumes "a \ Field r" and "b \ Field r"
shows "(max2 a b = b) = ((a,b) \ r)"
using assms ANTISYM unfolding antisym_def using TOTALS
unfolding max2_def by auto
subsubsection {* Existence and uniqueness for isMinim and well-definedness of minim *}
lemma isMinim_unique:
assumes MINIM: "isMinim B a" and MINIM': "isMinim B a'"
shows "a = a'"
proof-
{have "a \ B"
using MINIM isMinim_def by simp
hence "(a',a) \ r"
using MINIM' isMinim_def by simp
}
moreover
{have "a' \ B"
using MINIM' isMinim_def by simp
hence "(a,a') \ r"
using MINIM isMinim_def by simp
}
ultimately
show ?thesis using ANTISYM antisym_def[of r] by blast
qed
lemma Well_order_isMinim_exists:
assumes SUB: "B \ Field r" and NE: "B \ {}"
shows "\b. isMinim B b"
proof-
from spec[OF WF[unfolded wf_eq_minimal[of "r - Id"]], of B] NE obtain b where
*: "b \ B \ (\b'. b' \ b \ (b',b) \ r \ b' \ B)" by auto
show ?thesis
proof(simp add: isMinim_def, rule exI[of _ b], auto)
show "b \ B" using * by simp
next
fix b' assume As: "b' \ B"
hence **: "b \ Field r \ b' \ Field r" using As SUB * by auto
(* *)
from As * have "b' = b \ (b',b) \ r" by auto
moreover
{assume "b' = b"
hence "(b,b') \ r"
using ** REFL by (auto simp add: refl_on_def)
}
moreover
{assume "b' \ b \ (b',b) \ r"
hence "(b,b') \ r"
using ** TOTAL by (auto simp add: total_on_def)
}
ultimately show "(b,b') \ r" by blast
qed
qed
lemma minim_isMinim:
assumes SUB: "B \ Field r" and NE: "B \ {}"
shows "isMinim B (minim B)"
proof-
let ?phi = "(\ b. isMinim B b)"
from assms Well_order_isMinim_exists
obtain b where *: "?phi b" by blast
moreover
have "\ b'. ?phi b' \ b' = b"
using isMinim_unique * by auto
ultimately show ?thesis
unfolding minim_def using theI[of ?phi b] by blast
qed
subsubsection{* Properties of minim *}
lemma minim_in:
assumes "B \ Field r" and "B \ {}"
shows "minim B \ B"
proof-
from minim_isMinim[of B] assms
have "isMinim B (minim B)" by simp
thus ?thesis by (simp add: isMinim_def)
qed
lemma minim_inField:
assumes "B \ Field r" and "B \ {}"
shows "minim B \ Field r"
proof-
have "minim B \ B" using assms by (simp add: minim_in)
thus ?thesis using assms by blast
qed
lemma minim_least:
assumes SUB: "B \ Field r" and IN: "b \ B"
shows "(minim B, b) \ r"
proof-
from minim_isMinim[of B] assms
have "isMinim B (minim B)" by auto
thus ?thesis by (auto simp add: isMinim_def IN)
qed
lemma equals_minim:
assumes SUB: "B \ Field r" and IN: "a \ B" and
LEAST: "\ b. b \ B \ (a,b) \ r"
shows "a = minim B"
proof-
from minim_isMinim[of B] assms
have "isMinim B (minim B)" by auto
moreover have "isMinim B a" using IN LEAST isMinim_def by auto
ultimately show ?thesis
using isMinim_unique by auto
qed
subsubsection{* Properties of successor *}
lemma suc_AboveS:
assumes SUB: "B \ Field r" and ABOVES: "AboveS B \ {}"
shows "suc B \ AboveS B"
proof(unfold suc_def)
have "AboveS B \ Field r"
using AboveS_Field[of r] by auto
thus "minim (AboveS B) \ AboveS B"
using assms by (simp add: minim_in)
qed
lemma suc_greater:
assumes SUB: "B \ Field r" and ABOVES: "AboveS B \ {}" and
IN: "b \ B"
shows "suc B \ b \ (b,suc B) \ r"
proof-
from assms suc_AboveS
have "suc B \ AboveS B" by simp
with IN AboveS_def[of r] show ?thesis by simp
qed
lemma suc_least_AboveS:
assumes ABOVES: "a \ AboveS B"
shows "(suc B,a) \ r"
proof(unfold suc_def)
have "AboveS B \ Field r"
using AboveS_Field[of r] by auto
thus "(minim (AboveS B),a) \ r"
using assms minim_least by simp
qed
lemma suc_inField:
assumes "B \ Field r" and "AboveS B \ {}"
shows "suc B \ Field r"
proof-
have "suc B \ AboveS B" using suc_AboveS assms by simp
thus ?thesis
using assms AboveS_Field[of r] by auto
qed
lemma equals_suc_AboveS:
assumes SUB: "B \ Field r" and ABV: "a \ AboveS B" and
MINIM: "\ a'. a' \ AboveS B \ (a,a') \ r"
shows "a = suc B"
proof(unfold suc_def)
have "AboveS B \ Field r"
using AboveS_Field[of r B] by auto
thus "a = minim (AboveS B)"
using assms equals_minim
by simp
qed
lemma suc_underS:
assumes IN: "a \ Field r"
shows "a = suc (underS a)"
proof-
have "underS a \ Field r"
using underS_Field[of r] by auto
moreover
have "a \ AboveS (underS a)"
using in_AboveS_underS IN by fast
moreover
have "\a' \ AboveS (underS a). (a,a') \ r"
proof(clarify)
fix a'
assume *: "a' \ AboveS (underS a)"
hence **: "a' \ Field r"
using AboveS_Field by fast
{assume "(a,a') \ r"
hence "a' = a \ (a',a) \ r"
using TOTAL IN ** by (auto simp add: total_on_def)
moreover
{assume "a' = a"
hence "(a,a') \ r"
using REFL IN ** by (auto simp add: refl_on_def)
}
moreover
{assume "a' \ a \ (a',a) \ r"
hence "a' \ underS a"
unfolding underS_def by simp
hence "a' \ AboveS (underS a)"
using AboveS_disjoint by fast
with * have False by simp
}
ultimately have "(a,a') \ r" by blast
}
thus "(a, a') \ r" by blast
qed
ultimately show ?thesis
using equals_suc_AboveS by auto
qed
subsubsection {* Properties of order filters *}
lemma under_ofilter:
"ofilter (under a)"
proof(unfold ofilter_def under_def, auto simp add: Field_def)
fix aa x
assume "(aa,a) \ r" "(x,aa) \ r"
thus "(x,a) \ r"
using TRANS trans_def[of r] by blast
qed
lemma underS_ofilter:
"ofilter (underS a)"
proof(unfold ofilter_def underS_def under_def, auto simp add: Field_def)
fix aa assume "(a, aa) \ r" "(aa, a) \ r" and DIFF: "aa \ a"
thus False
using ANTISYM antisym_def[of r] by blast
next
fix aa x
assume "(aa,a) \ r" "aa \ a" "(x,aa) \ r"
thus "(x,a) \ r"
using TRANS trans_def[of r] by blast
qed
lemma Field_ofilter:
"ofilter (Field r)"
by(unfold ofilter_def under_def, auto simp add: Field_def)
lemma ofilter_underS_Field:
"ofilter A = ((\a \ Field r. A = underS a) \ (A = Field r))"
proof
assume "(\a\Field r. A = underS a) \ A = Field r"
thus "ofilter A"
by (auto simp: underS_ofilter Field_ofilter)
next
assume *: "ofilter A"
let ?One = "(\a\Field r. A = underS a)"
let ?Two = "(A = Field r)"
show "?One \ ?Two"
proof(cases ?Two, simp)
let ?B = "(Field r) - A"
let ?a = "minim ?B"
assume "A \ Field r"
moreover have "A \ Field r" using * ofilter_def by simp
ultimately have 1: "?B \ {}" by blast
hence 2: "?a \ Field r" using minim_inField[of ?B] by blast
have 3: "?a \ ?B" using minim_in[of ?B] 1 by blast
hence 4: "?a \ A" by blast
have 5: "A \ Field r" using * ofilter_def[of A] by auto
(* *)
moreover
have "A = underS ?a"
proof
show "A \ underS ?a"
proof(unfold underS_def, auto simp add: 4)
fix x assume **: "x \ A"
hence 11: "x \ Field r" using 5 by auto
have 12: "x \ ?a" using 4 ** by auto
have 13: "under x \ A" using * ofilter_def ** by auto
{assume "(x,?a) \ r"
hence "(?a,x) \ r"
using TOTAL total_on_def[of "Field r" r]
2 4 11 12 by auto
hence "?a \ under x" using under_def[of r] by auto
hence "?a \ A" using ** 13 by blast
with 4 have False by simp
}
thus "(x,?a) \ r" by blast
qed
next
show "underS ?a \ A"
proof(unfold underS_def, auto)
fix x
assume **: "x \ ?a" and ***: "(x,?a) \ r"
hence 11: "x \ Field r" using Field_def by fastforce
{assume "x \ A"
hence "x \ ?B" using 11 by auto
hence "(?a,x) \ r" using 3 minim_least[of ?B x] by blast
hence False
using ANTISYM antisym_def[of r] ** *** by auto
}
thus "x \ A" by blast
qed
qed
ultimately have ?One using 2 by blast
thus ?thesis by simp
qed
qed
lemma ofilter_UNION:
"(\ i. i \ I \ ofilter(A i)) \ ofilter (\