src/HOL/Fun.thy
 author bulwahn Wed, 19 Oct 2011 08:37:20 +0200 changeset 45174 10c3597f92f0 parent 44928 7ef6505bde7f child 45603 d2d9ef16ccaf permissions -rw-r--r--
removing old code generator setup for function types
```
(*  Title:      HOL/Fun.thy
Author:     Tobias Nipkow, Cambridge University Computer Laboratory
*)

theory Fun
imports Complete_Lattices
uses ("Tools/enriched_type.ML")
begin

lemma apply_inverse:
"f x = u \<Longrightarrow> (\<And>x. P x \<Longrightarrow> g (f x) = x) \<Longrightarrow> P x \<Longrightarrow> x = g u"
by auto

subsection {* The Identity Function @{text id} *}

definition id :: "'a \<Rightarrow> 'a" where
"id = (\<lambda>x. x)"

lemma id_apply [simp]: "id x = x"

lemma image_id [simp]: "id ` Y = Y"

lemma vimage_id [simp]: "id -` A = A"

subsection {* The Composition Operator @{text "f \<circ> g"} *}

definition comp :: "('b \<Rightarrow> 'c) \<Rightarrow> ('a \<Rightarrow> 'b) \<Rightarrow> 'a \<Rightarrow> 'c" (infixl "o" 55) where
"f o g = (\<lambda>x. f (g x))"

notation (xsymbols)
comp  (infixl "\<circ>" 55)

notation (HTML output)
comp  (infixl "\<circ>" 55)

lemma o_apply [simp]: "(f o g) x = f (g x)"

lemma o_assoc: "f o (g o h) = f o g o h"

lemma id_o [simp]: "id o g = g"

lemma o_id [simp]: "f o id = f"

lemma o_eq_dest:
"a o b = c o d \<Longrightarrow> a (b v) = c (d v)"
by (simp only: comp_def) (fact fun_cong)

lemma o_eq_elim:
"a o b = c o d \<Longrightarrow> ((\<And>v. a (b v) = c (d v)) \<Longrightarrow> R) \<Longrightarrow> R"
by (erule meta_mp) (fact o_eq_dest)

lemma image_compose: "(f o g) ` r = f`(g`r)"

lemma vimage_compose: "(g \<circ> f) -` x = f -` (g -` x)"
by auto

lemma UN_o: "UNION A (g o f) = UNION (f`A) g"
by (unfold comp_def, blast)

subsection {* The Forward Composition Operator @{text fcomp} *}

definition fcomp :: "('a \<Rightarrow> 'b) \<Rightarrow> ('b \<Rightarrow> 'c) \<Rightarrow> 'a \<Rightarrow> 'c" (infixl "\<circ>>" 60) where
"f \<circ>> g = (\<lambda>x. g (f x))"

lemma fcomp_apply [simp]:  "(f \<circ>> g) x = g (f x)"

lemma fcomp_assoc: "(f \<circ>> g) \<circ>> h = f \<circ>> (g \<circ>> h)"

lemma id_fcomp [simp]: "id \<circ>> g = g"

lemma fcomp_id [simp]: "f \<circ>> id = f"

code_const fcomp
(Eval infixl 1 "#>")

no_notation fcomp (infixl "\<circ>>" 60)

subsection {* Mapping functions *}

definition map_fun :: "('c \<Rightarrow> 'a) \<Rightarrow> ('b \<Rightarrow> 'd) \<Rightarrow> ('a \<Rightarrow> 'b) \<Rightarrow> 'c \<Rightarrow> 'd" where
"map_fun f g h = g \<circ> h \<circ> f"

lemma map_fun_apply [simp]:
"map_fun f g h x = g (h (f x))"

subsection {* Injectivity and Bijectivity *}

definition inj_on :: "('a \<Rightarrow> 'b) \<Rightarrow> 'a set \<Rightarrow> bool" where -- "injective"
"inj_on f A \<longleftrightarrow> (\<forall>x\<in>A. \<forall>y\<in>A. f x = f y \<longrightarrow> x = y)"

definition bij_betw :: "('a \<Rightarrow> 'b) \<Rightarrow> 'a set \<Rightarrow> 'b set \<Rightarrow> bool" where -- "bijective"
"bij_betw f A B \<longleftrightarrow> inj_on f A \<and> f ` A = B"

text{*A common special case: functions injective, surjective or bijective over
the entire domain type.*}

abbreviation
"inj f \<equiv> inj_on f UNIV"

abbreviation surj :: "('a \<Rightarrow> 'b) \<Rightarrow> bool" where -- "surjective"
"surj f \<equiv> (range f = UNIV)"

abbreviation
"bij f \<equiv> bij_betw f UNIV UNIV"

text{* The negated case: *}
translations
"\<not> CONST surj f" <= "CONST range f \<noteq> CONST UNIV"

lemma injI:
assumes "\<And>x y. f x = f y \<Longrightarrow> x = y"
shows "inj f"
using assms unfolding inj_on_def by auto

theorem range_ex1_eq: "inj f \<Longrightarrow> b : range f = (EX! x. b = f x)"
by (unfold inj_on_def, blast)

lemma injD: "[| inj(f); f(x) = f(y) |] ==> x=y"

lemma inj_on_eq_iff: "inj_on f A ==> x:A ==> y:A ==> (f(x) = f(y)) = (x=y)"

lemma inj_on_cong:
"(\<And> a. a : A \<Longrightarrow> f a = g a) \<Longrightarrow> inj_on f A = inj_on g A"
unfolding inj_on_def by auto

lemma inj_on_strict_subset:
"\<lbrakk> inj_on f B; A < B \<rbrakk> \<Longrightarrow> f`A < f`B"
unfolding inj_on_def unfolding image_def by blast

lemma inj_comp:
"inj f \<Longrightarrow> inj g \<Longrightarrow> inj (f \<circ> g)"

lemma inj_fun: "inj f \<Longrightarrow> inj (\<lambda>x y. f x)"

lemma inj_eq: "inj f ==> (f(x) = f(y)) = (x=y)"

lemma inj_on_id[simp]: "inj_on id A"

lemma inj_on_id2[simp]: "inj_on (%x. x) A"

lemma inj_on_Int: "\<lbrakk>inj_on f A; inj_on f B\<rbrakk> \<Longrightarrow> inj_on f (A \<inter> B)"
unfolding inj_on_def by blast

lemma inj_on_INTER:
"\<lbrakk>I \<noteq> {}; \<And> i. i \<in> I \<Longrightarrow> inj_on f (A i)\<rbrakk> \<Longrightarrow> inj_on f (\<Inter> i \<in> I. A i)"
unfolding inj_on_def by blast

lemma inj_on_Inter:
"\<lbrakk>S \<noteq> {}; \<And> A. A \<in> S \<Longrightarrow> inj_on f A\<rbrakk> \<Longrightarrow> inj_on f (Inter S)"
unfolding inj_on_def by blast

lemma inj_on_UNION_chain:
assumes CH: "\<And> i j. \<lbrakk>i \<in> I; j \<in> I\<rbrakk> \<Longrightarrow> A i \<le> A j \<or> A j \<le> A i" and
INJ: "\<And> i. i \<in> I \<Longrightarrow> inj_on f (A i)"
shows "inj_on f (\<Union> i \<in> I. A i)"
proof(unfold inj_on_def UNION_eq, auto)
fix i j x y
assume *: "i \<in> I" "j \<in> I" and **: "x \<in> A i" "y \<in> A j"
and ***: "f x = f y"
show "x = y"
proof-
{assume "A i \<le> A j"
with ** have "x \<in> A j" by auto
with INJ * ** *** have ?thesis
}
moreover
{assume "A j \<le> A i"
with ** have "y \<in> A i" by auto
with INJ * ** *** have ?thesis
}
ultimately show ?thesis using  CH * by blast
qed
qed

lemma surj_id: "surj id"
by simp

lemma bij_id[simp]: "bij id"

lemma inj_onI:
"(!! x y. [|  x:A;  y:A;  f(x) = f(y) |] ==> x=y) ==> inj_on f A"

lemma inj_on_inverseI: "(!!x. x:A ==> g(f(x)) = x) ==> inj_on f A"
by (auto dest:  arg_cong [of concl: g] simp add: inj_on_def)

lemma inj_onD: "[| inj_on f A;  f(x)=f(y);  x:A;  y:A |] ==> x=y"
by (unfold inj_on_def, blast)

lemma inj_on_iff: "[| inj_on f A;  x:A;  y:A |] ==> (f(x)=f(y)) = (x=y)"
by (blast dest!: inj_onD)

lemma comp_inj_on:
"[| inj_on f A;  inj_on g (f`A) |] ==> inj_on (g o f) A"

lemma inj_on_imageI: "inj_on (g o f) A \<Longrightarrow> inj_on g (f ` A)"
apply blast
done

lemma inj_on_image_iff: "\<lbrakk> ALL x:A. ALL y:A. (g(f x) = g(f y)) = (g x = g y);
inj_on f A \<rbrakk> \<Longrightarrow> inj_on g (f ` A) = inj_on g A"
apply(unfold inj_on_def)
apply blast
done

lemma inj_on_contraD: "[| inj_on f A;  ~x=y;  x:A;  y:A |] ==> ~ f(x)=f(y)"
by (unfold inj_on_def, blast)

lemma inj_singleton: "inj (%s. {s})"

lemma inj_on_empty[iff]: "inj_on f {}"

lemma subset_inj_on: "[| inj_on f B; A <= B |] ==> inj_on f A"
by (unfold inj_on_def, blast)

lemma inj_on_Un:
"inj_on f (A Un B) =
(inj_on f A & inj_on f B & f`(A-B) Int f`(B-A) = {})"
apply(unfold inj_on_def)
apply (blast intro:sym)
done

lemma inj_on_insert[iff]:
"inj_on f (insert a A) = (inj_on f A & f a ~: f`(A-{a}))"
apply(unfold inj_on_def)
apply (blast intro:sym)
done

lemma inj_on_diff: "inj_on f A ==> inj_on f (A-B)"
apply(unfold inj_on_def)
apply (blast)
done

lemma comp_inj_on_iff:
"inj_on f A \<Longrightarrow> inj_on f' (f ` A) \<longleftrightarrow> inj_on (f' o f) A"

lemma inj_on_imageI2:
"inj_on (f' o f) A \<Longrightarrow> inj_on f A"

lemma surj_def: "surj f \<longleftrightarrow> (\<forall>y. \<exists>x. y = f x)"
by auto

lemma surjI: assumes *: "\<And> x. g (f x) = x" shows "surj g"
using *[symmetric] by auto

lemma surjD: "surj f \<Longrightarrow> \<exists>x. y = f x"

lemma surjE: "surj f \<Longrightarrow> (\<And>x. y = f x \<Longrightarrow> C) \<Longrightarrow> C"

lemma comp_surj: "[| surj f;  surj g |] ==> surj (g o f)"
apply (simp add: comp_def surj_def, clarify)
apply (drule_tac x = y in spec, clarify)
apply (drule_tac x = x in spec, blast)
done

lemma bij_betw_imp_surj: "bij_betw f A UNIV \<Longrightarrow> surj f"
unfolding bij_betw_def by auto

lemma bij_betw_empty1:
assumes "bij_betw f {} A"
shows "A = {}"
using assms unfolding bij_betw_def by blast

lemma bij_betw_empty2:
assumes "bij_betw f A {}"
shows "A = {}"
using assms unfolding bij_betw_def by blast

lemma inj_on_imp_bij_betw:
"inj_on f A \<Longrightarrow> bij_betw f A (f ` A)"
unfolding bij_betw_def by simp

lemma bij_def: "bij f \<longleftrightarrow> inj f \<and> surj f"
unfolding bij_betw_def ..

lemma bijI: "[| inj f; surj f |] ==> bij f"

lemma bij_is_inj: "bij f ==> inj f"

lemma bij_is_surj: "bij f ==> surj f"

lemma bij_betw_imp_inj_on: "bij_betw f A B \<Longrightarrow> inj_on f A"

lemma bij_betw_trans:
"bij_betw f A B \<Longrightarrow> bij_betw g B C \<Longrightarrow> bij_betw (g o f) A C"

lemma bij_comp: "bij f \<Longrightarrow> bij g \<Longrightarrow> bij (g o f)"
by (rule bij_betw_trans)

lemma bij_betw_comp_iff:
"bij_betw f A A' \<Longrightarrow> bij_betw f' A' A'' \<longleftrightarrow> bij_betw (f' o f) A A''"

lemma bij_betw_comp_iff2:
assumes BIJ: "bij_betw f' A' A''" and IM: "f ` A \<le> A'"
shows "bij_betw f A A' \<longleftrightarrow> bij_betw (f' o f) A A''"
using assms
assume *: "bij_betw (f' \<circ> f) A A''"
thus "bij_betw f A A'"
using IM
assume "inj_on (f' \<circ> f) A"
thus "inj_on f A" using inj_on_imageI2 by blast
next
fix a' assume **: "a' \<in> A'"
hence "f' a' \<in> A''" using BIJ unfolding bij_betw_def by auto
then obtain a where 1: "a \<in> A \<and> f'(f a) = f' a'" using *
unfolding bij_betw_def by force
hence "f a \<in> A'" using IM by auto
hence "f a = a'" using BIJ ** 1 unfolding bij_betw_def inj_on_def by auto
thus "a' \<in> f ` A" using 1 by auto
qed
qed

lemma bij_betw_inv: assumes "bij_betw f A B" shows "EX g. bij_betw g B A"
proof -
have i: "inj_on f A" and s: "f ` A = B"
using assms by(auto simp:bij_betw_def)
let ?P = "%b a. a:A \<and> f a = b" let ?g = "%b. The (?P b)"
{ fix a b assume P: "?P b a"
hence ex1: "\<exists>a. ?P b a" using s unfolding image_def by blast
hence uex1: "\<exists>!a. ?P b a" by(blast dest:inj_onD[OF i])
hence " ?g b = a" using the1_equality[OF uex1, OF P] P by simp
} note g = this
have "inj_on ?g B"
proof(rule inj_onI)
fix x y assume "x:B" "y:B" "?g x = ?g y"
from s `x:B` obtain a1 where a1: "?P x a1" unfolding image_def by blast
from s `y:B` obtain a2 where a2: "?P y a2" unfolding image_def by blast
from g[OF a1] a1 g[OF a2] a2 `?g x = ?g y` show "x=y" by simp
qed
moreover have "?g ` B = A"
proof(auto simp:image_def)
fix b assume "b:B"
with s obtain a where P: "?P b a" unfolding image_def by blast
thus "?g b \<in> A" using g[OF P] by auto
next
fix a assume "a:A"
then obtain b where P: "?P b a" using s unfolding image_def by blast
then have "b:B" using s unfolding image_def by blast
with g[OF P] show "\<exists>b\<in>B. a = ?g b" by blast
qed
ultimately show ?thesis by(auto simp:bij_betw_def)
qed

lemma bij_betw_cong:
"(\<And> a. a \<in> A \<Longrightarrow> f a = g a) \<Longrightarrow> bij_betw f A A' = bij_betw g A A'"
unfolding bij_betw_def inj_on_def by force

lemma bij_betw_id[intro, simp]:
"bij_betw id A A"
unfolding bij_betw_def id_def by auto

lemma bij_betw_id_iff:
"bij_betw id A B \<longleftrightarrow> A = B"

lemma bij_betw_combine:
assumes "bij_betw f A B" "bij_betw f C D" "B \<inter> D = {}"
shows "bij_betw f (A \<union> C) (B \<union> D)"
using assms unfolding bij_betw_def inj_on_Un image_Un by auto

lemma bij_betw_UNION_chain:
assumes CH: "\<And> i j. \<lbrakk>i \<in> I; j \<in> I\<rbrakk> \<Longrightarrow> A i \<le> A j \<or> A j \<le> A i" and
BIJ: "\<And> i. i \<in> I \<Longrightarrow> bij_betw f (A i) (A' i)"
shows "bij_betw f (\<Union> i \<in> I. A i) (\<Union> i \<in> I. A' i)"
proof(unfold bij_betw_def, auto simp add: image_def)
have "\<And> i. i \<in> I \<Longrightarrow> inj_on f (A i)"
using BIJ bij_betw_def[of f] by auto
thus "inj_on f (\<Union> i \<in> I. A i)"
using CH inj_on_UNION_chain[of I A f] by auto
next
fix i x
assume *: "i \<in> I" "x \<in> A i"
hence "f x \<in> A' i" using BIJ bij_betw_def[of f] by auto
thus "\<exists>j \<in> I. f x \<in> A' j" using * by blast
next
fix i x'
assume *: "i \<in> I" "x' \<in> A' i"
hence "\<exists>x \<in> A i. x' = f x" using BIJ bij_betw_def[of f] by blast
thus "\<exists>j \<in> I. \<exists>x \<in> A j. x' = f x"
using * by blast
qed

lemma bij_betw_Disj_Un:
assumes DISJ: "A \<inter> B = {}" and DISJ': "A' \<inter> B' = {}" and
B1: "bij_betw f A A'" and B2: "bij_betw f B B'"
shows "bij_betw f (A \<union> B) (A' \<union> B')"
proof-
have 1: "inj_on f A \<and> inj_on f B"
using B1 B2 by (auto simp add: bij_betw_def)
have 2: "f`A = A' \<and> f`B = B'"
using B1 B2 by (auto simp add: bij_betw_def)
hence "f`(A - B) \<inter> f`(B - A) = {}"
using DISJ DISJ' by blast
hence "inj_on f (A \<union> B)"
using 1 by (auto simp add: inj_on_Un)
(*  *)
moreover
have "f`(A \<union> B) = A' \<union> B'"
using 2 by auto
ultimately show ?thesis
unfolding bij_betw_def by auto
qed

lemma bij_betw_subset:
assumes BIJ: "bij_betw f A A'" and
SUB: "B \<le> A" and IM: "f ` B = B'"
shows "bij_betw f B B'"
using assms
by(unfold bij_betw_def inj_on_def, auto simp add: inj_on_def)

lemma surj_image_vimage_eq: "surj f ==> f ` (f -` A) = A"
by simp

lemma surj_vimage_empty:
assumes "surj f" shows "f -` A = {} \<longleftrightarrow> A = {}"
using surj_image_vimage_eq[OF `surj f`, of A]
by (intro iffI) fastforce+

lemma inj_vimage_image_eq: "inj f ==> f -` (f ` A) = A"

lemma vimage_subsetD: "surj f ==> f -` B <= A ==> B <= f ` A"
by (blast intro: sym)

lemma vimage_subsetI: "inj f ==> B <= f ` A ==> f -` B <= A"
by (unfold inj_on_def, blast)

lemma vimage_subset_eq: "bij f ==> (f -` B <= A) = (B <= f ` A)"
apply (unfold bij_def)
apply (blast del: subsetI intro: vimage_subsetI vimage_subsetD)
done

lemma inj_on_Un_image_eq_iff: "inj_on f (A \<union> B) \<Longrightarrow> f ` A = f ` B \<longleftrightarrow> A = B"
by(blast dest: inj_onD)

lemma inj_on_image_Int:
"[| inj_on f C;  A<=C;  B<=C |] ==> f`(A Int B) = f`A Int f`B"
done

lemma inj_on_image_set_diff:
"[| inj_on f C;  A<=C;  B<=C |] ==> f`(A-B) = f`A - f`B"
done

lemma image_Int: "inj f ==> f`(A Int B) = f`A Int f`B"

lemma image_set_diff: "inj f ==> f`(A-B) = f`A - f`B"

lemma inj_image_mem_iff: "inj f ==> (f a : f`A) = (a : A)"
by (blast dest: injD)

lemma inj_image_subset_iff: "inj f ==> (f`A <= f`B) = (A<=B)"

lemma inj_image_eq_iff: "inj f ==> (f`A = f`B) = (A = B)"
by (blast dest: injD)

(*injectivity's required.  Left-to-right inclusion holds even if A is empty*)
lemma image_INT:
"[| inj_on f C;  ALL x:A. B x <= C;  j:A |]
==> f ` (INTER A B) = (INT x:A. f ` B x)"
done

(*Compare with image_INT: no use of inj_on, and if f is surjective then
it doesn't matter whether A is empty*)
lemma bij_image_INT: "bij f ==> f ` (INTER A B) = (INT x:A. f ` B x)"
apply (simp add: inj_on_def surj_def, blast)
done

lemma surj_Compl_image_subset: "surj f ==> -(f`A) <= f`(-A)"
by auto

lemma inj_image_Compl_subset: "inj f ==> f`(-A) <= -(f`A)"

lemma bij_image_Compl_eq: "bij f ==> f`(-A) = -(f`A)"
apply (rule equalityI)
apply (simp_all (no_asm_simp) add: inj_image_Compl_subset surj_Compl_image_subset)
done

lemma inj_vimage_singleton: "inj f \<Longrightarrow> f -` {a} \<subseteq> {THE x. f x = a}"
-- {* The inverse image of a singleton under an injective function
is included in a singleton. *}
apply (blast intro: the_equality [symmetric])
done

lemma inj_on_vimage_singleton:
"inj_on f A \<Longrightarrow> f -` {a} \<inter> A \<subseteq> {THE x. x \<in> A \<and> f x = a}"
by (auto simp add: inj_on_def intro: the_equality [symmetric])

lemma (in ordered_ab_group_add) inj_uminus[simp, intro]: "inj_on uminus A"
by (auto intro!: inj_onI)

lemma (in linorder) strict_mono_imp_inj_on: "strict_mono f \<Longrightarrow> inj_on f A"
by (auto intro!: inj_onI dest: strict_mono_eq)

subsection{*Function Updating*}

definition fun_upd :: "('a => 'b) => 'a => 'b => ('a => 'b)" where
"fun_upd f a b == % x. if x=a then b else f x"

nonterminal updbinds and updbind

syntax
"_updbind" :: "['a, 'a] => updbind"             ("(2_ :=/ _)")
""         :: "updbind => updbinds"             ("_")
"_updbinds":: "[updbind, updbinds] => updbinds" ("_,/ _")
"_Update"  :: "['a, updbinds] => 'a"            ("_/'((_)')" [1000, 0] 900)

translations
"_Update f (_updbinds b bs)" == "_Update (_Update f b) bs"
"f(x:=y)" == "CONST fun_upd f x y"

(* Hint: to define the sum of two functions (or maps), use sum_case.
A nice infix syntax could be defined (in Datatype.thy or below) by
notation
sum_case  (infixr "'(+')"80)
*)

lemma fun_upd_idem_iff: "(f(x:=y) = f) = (f x = y)"
apply (erule subst)
apply (rule_tac [2] ext, auto)
done

(* f x = y ==> f(x:=y) = f *)
lemmas fun_upd_idem = fun_upd_idem_iff [THEN iffD2, standard]

(* f(x := f x) = f *)
lemmas fun_upd_triv = refl [THEN fun_upd_idem]
declare fun_upd_triv [iff]

lemma fun_upd_apply [simp]: "(f(x:=y))z = (if z=x then y else f z)"

(* fun_upd_apply supersedes these two,   but they are useful
if fun_upd_apply is intentionally removed from the simpset *)
lemma fun_upd_same: "(f(x:=y)) x = y"
by simp

lemma fun_upd_other: "z~=x ==> (f(x:=y)) z = f z"
by simp

lemma fun_upd_upd [simp]: "f(x:=y,x:=z) = f(x:=z)"

lemma fun_upd_twist: "a ~= c ==> (m(a:=b))(c:=d) = (m(c:=d))(a:=b)"
by (rule ext, auto)

lemma inj_on_fun_updI: "\<lbrakk> inj_on f A; y \<notin> f`A \<rbrakk> \<Longrightarrow> inj_on (f(x:=y)) A"
by (fastforce simp:inj_on_def image_def)

lemma fun_upd_image:
"f(x:=y) ` A = (if x \<in> A then insert y (f ` (A-{x})) else f ` A)"
by auto

lemma fun_upd_comp: "f \<circ> (g(x := y)) = (f \<circ> g)(x := f y)"
by auto

lemma UNION_fun_upd:
"UNION J (A(i:=B)) = (UNION (J-{i}) A \<union> (if i\<in>J then B else {}))"
by (auto split: if_splits)

subsection {* @{text override_on} *}

definition override_on :: "('a \<Rightarrow> 'b) \<Rightarrow> ('a \<Rightarrow> 'b) \<Rightarrow> 'a set \<Rightarrow> 'a \<Rightarrow> 'b" where
"override_on f g A = (\<lambda>a. if a \<in> A then g a else f a)"

lemma override_on_emptyset[simp]: "override_on f g {} = f"

lemma override_on_apply_notin[simp]: "a ~: A ==> (override_on f g A) a = f a"

lemma override_on_apply_in[simp]: "a : A ==> (override_on f g A) a = g a"

subsection {* @{text swap} *}

definition swap :: "'a \<Rightarrow> 'a \<Rightarrow> ('a \<Rightarrow> 'b) \<Rightarrow> ('a \<Rightarrow> 'b)" where
"swap a b f = f (a := f b, b:= f a)"

lemma swap_self [simp]: "swap a a f = f"

lemma swap_commute: "swap a b f = swap b a f"
by (rule ext, simp add: fun_upd_def swap_def)

lemma swap_nilpotent [simp]: "swap a b (swap a b f) = f"
by (rule ext, simp add: fun_upd_def swap_def)

lemma swap_triple:
assumes "a \<noteq> c" and "b \<noteq> c"
shows "swap a b (swap b c (swap a b f)) = swap a c f"
using assms by (simp add: fun_eq_iff swap_def)

lemma comp_swap: "f \<circ> swap a b g = swap a b (f \<circ> g)"
by (rule ext, simp add: fun_upd_def swap_def)

lemma swap_image_eq [simp]:
assumes "a \<in> A" "b \<in> A" shows "swap a b f ` A = f ` A"
proof -
have subset: "\<And>f. swap a b f ` A \<subseteq> f ` A"
using assms by (auto simp: image_iff swap_def)
then have "swap a b (swap a b f) ` A \<subseteq> (swap a b f) ` A" .
with subset[of f] show ?thesis by auto
qed

lemma inj_on_imp_inj_on_swap:
"\<lbrakk>inj_on f A; a \<in> A; b \<in> A\<rbrakk> \<Longrightarrow> inj_on (swap a b f) A"
by (simp add: inj_on_def swap_def, blast)

lemma inj_on_swap_iff [simp]:
assumes A: "a \<in> A" "b \<in> A" shows "inj_on (swap a b f) A \<longleftrightarrow> inj_on f A"
proof
assume "inj_on (swap a b f) A"
with A have "inj_on (swap a b (swap a b f)) A"
by (iprover intro: inj_on_imp_inj_on_swap)
thus "inj_on f A" by simp
next
assume "inj_on f A"
with A show "inj_on (swap a b f) A" by (iprover intro: inj_on_imp_inj_on_swap)
qed

lemma surj_imp_surj_swap: "surj f \<Longrightarrow> surj (swap a b f)"
by simp

lemma surj_swap_iff [simp]: "surj (swap a b f) \<longleftrightarrow> surj f"
by simp

lemma bij_betw_swap_iff [simp]:
"\<lbrakk> x \<in> A; y \<in> A \<rbrakk> \<Longrightarrow> bij_betw (swap x y f) A B \<longleftrightarrow> bij_betw f A B"
by (auto simp: bij_betw_def)

lemma bij_swap_iff [simp]: "bij (swap a b f) \<longleftrightarrow> bij f"
by simp

hide_const (open) swap

subsection {* Inversion of injective functions *}

definition the_inv_into :: "'a set => ('a => 'b) => ('b => 'a)" where
"the_inv_into A f == %x. THE y. y : A & f y = x"

lemma the_inv_into_f_f:
"[| inj_on f A;  x : A |] ==> the_inv_into A f (f x) = x"
apply blast
done

lemma f_the_inv_into_f:
"inj_on f A ==> y : f`A  ==> f (the_inv_into A f y) = y"
apply (rule the1I2)
apply(blast dest: inj_onD)
apply blast
done

lemma the_inv_into_into:
"[| inj_on f A; x : f ` A; A <= B |] ==> the_inv_into A f x : B"
apply (rule the1I2)
apply(blast dest: inj_onD)
apply blast
done

lemma the_inv_into_onto[simp]:
"inj_on f A ==> the_inv_into A f ` (f ` A) = A"
by (fast intro:the_inv_into_into the_inv_into_f_f[symmetric])

lemma the_inv_into_f_eq:
"[| inj_on f A; f x = y; x : A |] ==> the_inv_into A f y = x"
apply (erule subst)
apply (erule the_inv_into_f_f, assumption)
done

lemma the_inv_into_comp:
"[| inj_on f (g ` A); inj_on g A; x : f ` g ` A |] ==>
the_inv_into A (f o g) x = (the_inv_into A g o the_inv_into (g ` A) f) x"
apply (rule the_inv_into_f_eq)
apply (fast intro: comp_inj_on)
done

lemma inj_on_the_inv_into:
"inj_on f A \<Longrightarrow> inj_on (the_inv_into A f) (f ` A)"
by (auto intro: inj_onI simp: image_def the_inv_into_f_f)

lemma bij_betw_the_inv_into:
"bij_betw f A B \<Longrightarrow> bij_betw (the_inv_into A f) B A"
by (auto simp add: bij_betw_def inj_on_the_inv_into the_inv_into_into)

abbreviation the_inv :: "('a \<Rightarrow> 'b) \<Rightarrow> ('b \<Rightarrow> 'a)" where
"the_inv f \<equiv> the_inv_into UNIV f"

lemma the_inv_f_f:
assumes "inj f"
shows "the_inv f (f x) = x" using assms UNIV_I
by (rule the_inv_into_f_f)

text{*compatibility*}
lemmas o_def = comp_def

"\<not>(\<exists>f. f ` A = Pow A)"
proof clarify
fix f assume "f ` A = Pow A" hence *: "Pow A \<le> f ` A" by blast
let ?X = "{a \<in> A. a \<notin> f a}"
have "?X \<in> Pow A" unfolding Pow_def by auto
with * obtain x where "x \<in> A \<and> f x = ?X" by blast
thus False by best
qed

subsection {* Setup *}

subsubsection {* Proof tools *}

text {* simplifies terms of the form
f(...,x:=y,...,x:=z,...) to f(...,x:=z,...) *}

simproc_setup fun_upd2 ("f(v := w, x := y)") = {* fn _ =>
let
fun gen_fun_upd NONE T _ _ = NONE
| gen_fun_upd (SOME f) T x y = SOME (Const (@{const_name fun_upd}, T) \$ f \$ x \$ y)
fun dest_fun_T1 (Type (_, T :: Ts)) = T
fun find_double (t as Const (@{const_name fun_upd},T) \$ f \$ x \$ y) =
let
fun find (Const (@{const_name fun_upd},T) \$ g \$ v \$ w) =
if v aconv x then SOME g else gen_fun_upd (find g) T v w
| find t = NONE
in (dest_fun_T1 T, gen_fun_upd (find f) T x y) end

fun proc ss ct =
let
val ctxt = Simplifier.the_context ss
val t = Thm.term_of ct
in
case find_double t of
(T, NONE) => NONE
| (T, SOME rhs) =>
SOME (Goal.prove ctxt [] [] (Logic.mk_equals (t, rhs))
(fn _ =>
rtac eq_reflection 1 THEN
rtac ext 1 THEN
simp_tac (Simplifier.inherit_context ss @{simpset}) 1))
end
in proc end
*}

subsubsection {* Code generator *}

code_const "op \<circ>"
(SML infixl 5 "o")