src/HOL/Fun.thy
 author wenzelm Mon Mar 22 20:58:52 2010 +0100 (2010-03-22) changeset 35898 c890a3835d15 parent 35584 768f8d92b767 child 36176 3fe7e97ccca8 permissions -rw-r--r--
```     1 (*  Title:      HOL/Fun.thy
```
```     2     Author:     Tobias Nipkow, Cambridge University Computer Laboratory
```
```     3     Copyright   1994  University of Cambridge
```
```     4 *)
```
```     5
```
```     6 header {* Notions about functions *}
```
```     7
```
```     8 theory Fun
```
```     9 imports Complete_Lattice
```
```    10 begin
```
```    11
```
```    12 text{*As a simplification rule, it replaces all function equalities by
```
```    13   first-order equalities.*}
```
```    14 lemma expand_fun_eq: "f = g \<longleftrightarrow> (\<forall>x. f x = g x)"
```
```    15 apply (rule iffI)
```
```    16 apply (simp (no_asm_simp))
```
```    17 apply (rule ext)
```
```    18 apply (simp (no_asm_simp))
```
```    19 done
```
```    20
```
```    21 lemma apply_inverse:
```
```    22   "f x = u \<Longrightarrow> (\<And>x. P x \<Longrightarrow> g (f x) = x) \<Longrightarrow> P x \<Longrightarrow> x = g u"
```
```    23   by auto
```
```    24
```
```    25
```
```    26 subsection {* The Identity Function @{text id} *}
```
```    27
```
```    28 definition
```
```    29   id :: "'a \<Rightarrow> 'a"
```
```    30 where
```
```    31   "id = (\<lambda>x. x)"
```
```    32
```
```    33 lemma id_apply [simp]: "id x = x"
```
```    34   by (simp add: id_def)
```
```    35
```
```    36 lemma image_ident [simp]: "(%x. x) ` Y = Y"
```
```    37 by blast
```
```    38
```
```    39 lemma image_id [simp]: "id ` Y = Y"
```
```    40 by (simp add: id_def)
```
```    41
```
```    42 lemma vimage_ident [simp]: "(%x. x) -` Y = Y"
```
```    43 by blast
```
```    44
```
```    45 lemma vimage_id [simp]: "id -` A = A"
```
```    46 by (simp add: id_def)
```
```    47
```
```    48
```
```    49 subsection {* The Composition Operator @{text "f \<circ> g"} *}
```
```    50
```
```    51 definition
```
```    52   comp :: "('b \<Rightarrow> 'c) \<Rightarrow> ('a \<Rightarrow> 'b) \<Rightarrow> 'a \<Rightarrow> 'c" (infixl "o" 55)
```
```    53 where
```
```    54   "f o g = (\<lambda>x. f (g x))"
```
```    55
```
```    56 notation (xsymbols)
```
```    57   comp  (infixl "\<circ>" 55)
```
```    58
```
```    59 notation (HTML output)
```
```    60   comp  (infixl "\<circ>" 55)
```
```    61
```
```    62 text{*compatibility*}
```
```    63 lemmas o_def = comp_def
```
```    64
```
```    65 lemma o_apply [simp]: "(f o g) x = f (g x)"
```
```    66 by (simp add: comp_def)
```
```    67
```
```    68 lemma o_assoc: "f o (g o h) = f o g o h"
```
```    69 by (simp add: comp_def)
```
```    70
```
```    71 lemma id_o [simp]: "id o g = g"
```
```    72 by (simp add: comp_def)
```
```    73
```
```    74 lemma o_id [simp]: "f o id = f"
```
```    75 by (simp add: comp_def)
```
```    76
```
```    77 lemma o_eq_dest:
```
```    78   "a o b = c o d \<Longrightarrow> a (b v) = c (d v)"
```
```    79   by (simp only: o_def) (fact fun_cong)
```
```    80
```
```    81 lemma o_eq_elim:
```
```    82   "a o b = c o d \<Longrightarrow> ((\<And>v. a (b v) = c (d v)) \<Longrightarrow> R) \<Longrightarrow> R"
```
```    83   by (erule meta_mp) (fact o_eq_dest)
```
```    84
```
```    85 lemma image_compose: "(f o g) ` r = f`(g`r)"
```
```    86 by (simp add: comp_def, blast)
```
```    87
```
```    88 lemma vimage_compose: "(g \<circ> f) -` x = f -` (g -` x)"
```
```    89   by auto
```
```    90
```
```    91 lemma UN_o: "UNION A (g o f) = UNION (f`A) g"
```
```    92 by (unfold comp_def, blast)
```
```    93
```
```    94
```
```    95 subsection {* The Forward Composition Operator @{text fcomp} *}
```
```    96
```
```    97 definition
```
```    98   fcomp :: "('a \<Rightarrow> 'b) \<Rightarrow> ('b \<Rightarrow> 'c) \<Rightarrow> 'a \<Rightarrow> 'c" (infixl "o>" 60)
```
```    99 where
```
```   100   "f o> g = (\<lambda>x. g (f x))"
```
```   101
```
```   102 lemma fcomp_apply:  "(f o> g) x = g (f x)"
```
```   103   by (simp add: fcomp_def)
```
```   104
```
```   105 lemma fcomp_assoc: "(f o> g) o> h = f o> (g o> h)"
```
```   106   by (simp add: fcomp_def)
```
```   107
```
```   108 lemma id_fcomp [simp]: "id o> g = g"
```
```   109   by (simp add: fcomp_def)
```
```   110
```
```   111 lemma fcomp_id [simp]: "f o> id = f"
```
```   112   by (simp add: fcomp_def)
```
```   113
```
```   114 code_const fcomp
```
```   115   (Eval infixl 1 "#>")
```
```   116
```
```   117 no_notation fcomp (infixl "o>" 60)
```
```   118
```
```   119
```
```   120 subsection {* Injectivity and Surjectivity *}
```
```   121
```
```   122 definition
```
```   123   inj_on :: "['a => 'b, 'a set] => bool" where
```
```   124   -- "injective"
```
```   125   "inj_on f A == ! x:A. ! y:A. f(x)=f(y) --> x=y"
```
```   126
```
```   127 text{*A common special case: functions injective over the entire domain type.*}
```
```   128
```
```   129 abbreviation
```
```   130   "inj f == inj_on f UNIV"
```
```   131
```
```   132 definition
```
```   133   bij_betw :: "('a => 'b) => 'a set => 'b set => bool" where -- "bijective"
```
```   134   [code del]: "bij_betw f A B \<longleftrightarrow> inj_on f A & f ` A = B"
```
```   135
```
```   136 definition
```
```   137   surj :: "('a => 'b) => bool" where
```
```   138   -- "surjective"
```
```   139   "surj f == ! y. ? x. y=f(x)"
```
```   140
```
```   141 definition
```
```   142   bij :: "('a => 'b) => bool" where
```
```   143   -- "bijective"
```
```   144   "bij f == inj f & surj f"
```
```   145
```
```   146 lemma injI:
```
```   147   assumes "\<And>x y. f x = f y \<Longrightarrow> x = y"
```
```   148   shows "inj f"
```
```   149   using assms unfolding inj_on_def by auto
```
```   150
```
```   151 text{*For Proofs in @{text "Tools/Datatype/datatype_rep_proofs"}*}
```
```   152 lemma datatype_injI:
```
```   153     "(!! x. ALL y. f(x) = f(y) --> x=y) ==> inj(f)"
```
```   154 by (simp add: inj_on_def)
```
```   155
```
```   156 theorem range_ex1_eq: "inj f \<Longrightarrow> b : range f = (EX! x. b = f x)"
```
```   157   by (unfold inj_on_def, blast)
```
```   158
```
```   159 lemma injD: "[| inj(f); f(x) = f(y) |] ==> x=y"
```
```   160 by (simp add: inj_on_def)
```
```   161
```
```   162 lemma inj_on_eq_iff: "inj_on f A ==> x:A ==> y:A ==> (f(x) = f(y)) = (x=y)"
```
```   163 by (force simp add: inj_on_def)
```
```   164
```
```   165 lemma inj_eq: "inj f ==> (f(x) = f(y)) = (x=y)"
```
```   166 by (simp add: inj_on_eq_iff)
```
```   167
```
```   168 lemma inj_on_id[simp]: "inj_on id A"
```
```   169   by (simp add: inj_on_def)
```
```   170
```
```   171 lemma inj_on_id2[simp]: "inj_on (%x. x) A"
```
```   172 by (simp add: inj_on_def)
```
```   173
```
```   174 lemma surj_id[simp]: "surj id"
```
```   175 by (simp add: surj_def)
```
```   176
```
```   177 lemma bij_id[simp]: "bij id"
```
```   178 by (simp add: bij_def)
```
```   179
```
```   180 lemma inj_onI:
```
```   181     "(!! x y. [|  x:A;  y:A;  f(x) = f(y) |] ==> x=y) ==> inj_on f A"
```
```   182 by (simp add: inj_on_def)
```
```   183
```
```   184 lemma inj_on_inverseI: "(!!x. x:A ==> g(f(x)) = x) ==> inj_on f A"
```
```   185 by (auto dest:  arg_cong [of concl: g] simp add: inj_on_def)
```
```   186
```
```   187 lemma inj_onD: "[| inj_on f A;  f(x)=f(y);  x:A;  y:A |] ==> x=y"
```
```   188 by (unfold inj_on_def, blast)
```
```   189
```
```   190 lemma inj_on_iff: "[| inj_on f A;  x:A;  y:A |] ==> (f(x)=f(y)) = (x=y)"
```
```   191 by (blast dest!: inj_onD)
```
```   192
```
```   193 lemma comp_inj_on:
```
```   194      "[| inj_on f A;  inj_on g (f`A) |] ==> inj_on (g o f) A"
```
```   195 by (simp add: comp_def inj_on_def)
```
```   196
```
```   197 lemma inj_on_imageI: "inj_on (g o f) A \<Longrightarrow> inj_on g (f ` A)"
```
```   198 apply(simp add:inj_on_def image_def)
```
```   199 apply blast
```
```   200 done
```
```   201
```
```   202 lemma inj_on_image_iff: "\<lbrakk> ALL x:A. ALL y:A. (g(f x) = g(f y)) = (g x = g y);
```
```   203   inj_on f A \<rbrakk> \<Longrightarrow> inj_on g (f ` A) = inj_on g A"
```
```   204 apply(unfold inj_on_def)
```
```   205 apply blast
```
```   206 done
```
```   207
```
```   208 lemma inj_on_contraD: "[| inj_on f A;  ~x=y;  x:A;  y:A |] ==> ~ f(x)=f(y)"
```
```   209 by (unfold inj_on_def, blast)
```
```   210
```
```   211 lemma inj_singleton: "inj (%s. {s})"
```
```   212 by (simp add: inj_on_def)
```
```   213
```
```   214 lemma inj_on_empty[iff]: "inj_on f {}"
```
```   215 by(simp add: inj_on_def)
```
```   216
```
```   217 lemma subset_inj_on: "[| inj_on f B; A <= B |] ==> inj_on f A"
```
```   218 by (unfold inj_on_def, blast)
```
```   219
```
```   220 lemma inj_on_Un:
```
```   221  "inj_on f (A Un B) =
```
```   222   (inj_on f A & inj_on f B & f`(A-B) Int f`(B-A) = {})"
```
```   223 apply(unfold inj_on_def)
```
```   224 apply (blast intro:sym)
```
```   225 done
```
```   226
```
```   227 lemma inj_on_insert[iff]:
```
```   228   "inj_on f (insert a A) = (inj_on f A & f a ~: f`(A-{a}))"
```
```   229 apply(unfold inj_on_def)
```
```   230 apply (blast intro:sym)
```
```   231 done
```
```   232
```
```   233 lemma inj_on_diff: "inj_on f A ==> inj_on f (A-B)"
```
```   234 apply(unfold inj_on_def)
```
```   235 apply (blast)
```
```   236 done
```
```   237
```
```   238 lemma surjI: "(!! x. g(f x) = x) ==> surj g"
```
```   239 apply (simp add: surj_def)
```
```   240 apply (blast intro: sym)
```
```   241 done
```
```   242
```
```   243 lemma surj_range: "surj f ==> range f = UNIV"
```
```   244 by (auto simp add: surj_def)
```
```   245
```
```   246 lemma surjD: "surj f ==> EX x. y = f x"
```
```   247 by (simp add: surj_def)
```
```   248
```
```   249 lemma surjE: "surj f ==> (!!x. y = f x ==> C) ==> C"
```
```   250 by (simp add: surj_def, blast)
```
```   251
```
```   252 lemma comp_surj: "[| surj f;  surj g |] ==> surj (g o f)"
```
```   253 apply (simp add: comp_def surj_def, clarify)
```
```   254 apply (drule_tac x = y in spec, clarify)
```
```   255 apply (drule_tac x = x in spec, blast)
```
```   256 done
```
```   257
```
```   258 lemma bijI: "[| inj f; surj f |] ==> bij f"
```
```   259 by (simp add: bij_def)
```
```   260
```
```   261 lemma bij_is_inj: "bij f ==> inj f"
```
```   262 by (simp add: bij_def)
```
```   263
```
```   264 lemma bij_is_surj: "bij f ==> surj f"
```
```   265 by (simp add: bij_def)
```
```   266
```
```   267 lemma bij_betw_imp_inj_on: "bij_betw f A B \<Longrightarrow> inj_on f A"
```
```   268 by (simp add: bij_betw_def)
```
```   269
```
```   270 lemma bij_comp: "bij f \<Longrightarrow> bij g \<Longrightarrow> bij (g o f)"
```
```   271 by(fastsimp intro: comp_inj_on comp_surj simp: bij_def surj_range)
```
```   272
```
```   273 lemma bij_betw_trans:
```
```   274   "bij_betw f A B \<Longrightarrow> bij_betw g B C \<Longrightarrow> bij_betw (g o f) A C"
```
```   275 by(auto simp add:bij_betw_def comp_inj_on)
```
```   276
```
```   277 lemma bij_betw_inv: assumes "bij_betw f A B" shows "EX g. bij_betw g B A"
```
```   278 proof -
```
```   279   have i: "inj_on f A" and s: "f ` A = B"
```
```   280     using assms by(auto simp:bij_betw_def)
```
```   281   let ?P = "%b a. a:A \<and> f a = b" let ?g = "%b. The (?P b)"
```
```   282   { fix a b assume P: "?P b a"
```
```   283     hence ex1: "\<exists>a. ?P b a" using s unfolding image_def by blast
```
```   284     hence uex1: "\<exists>!a. ?P b a" by(blast dest:inj_onD[OF i])
```
```   285     hence " ?g b = a" using the1_equality[OF uex1, OF P] P by simp
```
```   286   } note g = this
```
```   287   have "inj_on ?g B"
```
```   288   proof(rule inj_onI)
```
```   289     fix x y assume "x:B" "y:B" "?g x = ?g y"
```
```   290     from s `x:B` obtain a1 where a1: "?P x a1" unfolding image_def by blast
```
```   291     from s `y:B` obtain a2 where a2: "?P y a2" unfolding image_def by blast
```
```   292     from g[OF a1] a1 g[OF a2] a2 `?g x = ?g y` show "x=y" by simp
```
```   293   qed
```
```   294   moreover have "?g ` B = A"
```
```   295   proof(auto simp:image_def)
```
```   296     fix b assume "b:B"
```
```   297     with s obtain a where P: "?P b a" unfolding image_def by blast
```
```   298     thus "?g b \<in> A" using g[OF P] by auto
```
```   299   next
```
```   300     fix a assume "a:A"
```
```   301     then obtain b where P: "?P b a" using s unfolding image_def by blast
```
```   302     then have "b:B" using s unfolding image_def by blast
```
```   303     with g[OF P] show "\<exists>b\<in>B. a = ?g b" by blast
```
```   304   qed
```
```   305   ultimately show ?thesis by(auto simp:bij_betw_def)
```
```   306 qed
```
```   307
```
```   308 lemma surj_image_vimage_eq: "surj f ==> f ` (f -` A) = A"
```
```   309 by (simp add: surj_range)
```
```   310
```
```   311 lemma inj_vimage_image_eq: "inj f ==> f -` (f ` A) = A"
```
```   312 by (simp add: inj_on_def, blast)
```
```   313
```
```   314 lemma vimage_subsetD: "surj f ==> f -` B <= A ==> B <= f ` A"
```
```   315 apply (unfold surj_def)
```
```   316 apply (blast intro: sym)
```
```   317 done
```
```   318
```
```   319 lemma vimage_subsetI: "inj f ==> B <= f ` A ==> f -` B <= A"
```
```   320 by (unfold inj_on_def, blast)
```
```   321
```
```   322 lemma vimage_subset_eq: "bij f ==> (f -` B <= A) = (B <= f ` A)"
```
```   323 apply (unfold bij_def)
```
```   324 apply (blast del: subsetI intro: vimage_subsetI vimage_subsetD)
```
```   325 done
```
```   326
```
```   327 lemma inj_on_Un_image_eq_iff: "inj_on f (A \<union> B) \<Longrightarrow> f ` A = f ` B \<longleftrightarrow> A = B"
```
```   328 by(blast dest: inj_onD)
```
```   329
```
```   330 lemma inj_on_image_Int:
```
```   331    "[| inj_on f C;  A<=C;  B<=C |] ==> f`(A Int B) = f`A Int f`B"
```
```   332 apply (simp add: inj_on_def, blast)
```
```   333 done
```
```   334
```
```   335 lemma inj_on_image_set_diff:
```
```   336    "[| inj_on f C;  A<=C;  B<=C |] ==> f`(A-B) = f`A - f`B"
```
```   337 apply (simp add: inj_on_def, blast)
```
```   338 done
```
```   339
```
```   340 lemma image_Int: "inj f ==> f`(A Int B) = f`A Int f`B"
```
```   341 by (simp add: inj_on_def, blast)
```
```   342
```
```   343 lemma image_set_diff: "inj f ==> f`(A-B) = f`A - f`B"
```
```   344 by (simp add: inj_on_def, blast)
```
```   345
```
```   346 lemma inj_image_mem_iff: "inj f ==> (f a : f`A) = (a : A)"
```
```   347 by (blast dest: injD)
```
```   348
```
```   349 lemma inj_image_subset_iff: "inj f ==> (f`A <= f`B) = (A<=B)"
```
```   350 by (simp add: inj_on_def, blast)
```
```   351
```
```   352 lemma inj_image_eq_iff: "inj f ==> (f`A = f`B) = (A = B)"
```
```   353 by (blast dest: injD)
```
```   354
```
```   355 (*injectivity's required.  Left-to-right inclusion holds even if A is empty*)
```
```   356 lemma image_INT:
```
```   357    "[| inj_on f C;  ALL x:A. B x <= C;  j:A |]
```
```   358     ==> f ` (INTER A B) = (INT x:A. f ` B x)"
```
```   359 apply (simp add: inj_on_def, blast)
```
```   360 done
```
```   361
```
```   362 (*Compare with image_INT: no use of inj_on, and if f is surjective then
```
```   363   it doesn't matter whether A is empty*)
```
```   364 lemma bij_image_INT: "bij f ==> f ` (INTER A B) = (INT x:A. f ` B x)"
```
```   365 apply (simp add: bij_def)
```
```   366 apply (simp add: inj_on_def surj_def, blast)
```
```   367 done
```
```   368
```
```   369 lemma surj_Compl_image_subset: "surj f ==> -(f`A) <= f`(-A)"
```
```   370 by (auto simp add: surj_def)
```
```   371
```
```   372 lemma inj_image_Compl_subset: "inj f ==> f`(-A) <= -(f`A)"
```
```   373 by (auto simp add: inj_on_def)
```
```   374
```
```   375 lemma bij_image_Compl_eq: "bij f ==> f`(-A) = -(f`A)"
```
```   376 apply (simp add: bij_def)
```
```   377 apply (rule equalityI)
```
```   378 apply (simp_all (no_asm_simp) add: inj_image_Compl_subset surj_Compl_image_subset)
```
```   379 done
```
```   380
```
```   381 lemma (in ordered_ab_group_add) inj_uminus[simp, intro]: "inj_on uminus A"
```
```   382   by (auto intro!: inj_onI)
```
```   383
```
```   384 lemma (in linorder) strict_mono_imp_inj_on: "strict_mono f \<Longrightarrow> inj_on f A"
```
```   385   by (auto intro!: inj_onI dest: strict_mono_eq)
```
```   386
```
```   387 subsection{*Function Updating*}
```
```   388
```
```   389 definition
```
```   390   fun_upd :: "('a => 'b) => 'a => 'b => ('a => 'b)" where
```
```   391   "fun_upd f a b == % x. if x=a then b else f x"
```
```   392
```
```   393 nonterminals
```
```   394   updbinds updbind
```
```   395 syntax
```
```   396   "_updbind" :: "['a, 'a] => updbind"             ("(2_ :=/ _)")
```
```   397   ""         :: "updbind => updbinds"             ("_")
```
```   398   "_updbinds":: "[updbind, updbinds] => updbinds" ("_,/ _")
```
```   399   "_Update"  :: "['a, updbinds] => 'a"            ("_/'((_)')" [1000, 0] 900)
```
```   400
```
```   401 translations
```
```   402   "_Update f (_updbinds b bs)" == "_Update (_Update f b) bs"
```
```   403   "f(x:=y)" == "CONST fun_upd f x y"
```
```   404
```
```   405 (* Hint: to define the sum of two functions (or maps), use sum_case.
```
```   406          A nice infix syntax could be defined (in Datatype.thy or below) by
```
```   407 notation
```
```   408   sum_case  (infixr "'(+')"80)
```
```   409 *)
```
```   410
```
```   411 lemma fun_upd_idem_iff: "(f(x:=y) = f) = (f x = y)"
```
```   412 apply (simp add: fun_upd_def, safe)
```
```   413 apply (erule subst)
```
```   414 apply (rule_tac [2] ext, auto)
```
```   415 done
```
```   416
```
```   417 (* f x = y ==> f(x:=y) = f *)
```
```   418 lemmas fun_upd_idem = fun_upd_idem_iff [THEN iffD2, standard]
```
```   419
```
```   420 (* f(x := f x) = f *)
```
```   421 lemmas fun_upd_triv = refl [THEN fun_upd_idem]
```
```   422 declare fun_upd_triv [iff]
```
```   423
```
```   424 lemma fun_upd_apply [simp]: "(f(x:=y))z = (if z=x then y else f z)"
```
```   425 by (simp add: fun_upd_def)
```
```   426
```
```   427 (* fun_upd_apply supersedes these two,   but they are useful
```
```   428    if fun_upd_apply is intentionally removed from the simpset *)
```
```   429 lemma fun_upd_same: "(f(x:=y)) x = y"
```
```   430 by simp
```
```   431
```
```   432 lemma fun_upd_other: "z~=x ==> (f(x:=y)) z = f z"
```
```   433 by simp
```
```   434
```
```   435 lemma fun_upd_upd [simp]: "f(x:=y,x:=z) = f(x:=z)"
```
```   436 by (simp add: expand_fun_eq)
```
```   437
```
```   438 lemma fun_upd_twist: "a ~= c ==> (m(a:=b))(c:=d) = (m(c:=d))(a:=b)"
```
```   439 by (rule ext, auto)
```
```   440
```
```   441 lemma inj_on_fun_updI: "\<lbrakk> inj_on f A; y \<notin> f`A \<rbrakk> \<Longrightarrow> inj_on (f(x:=y)) A"
```
```   442 by (fastsimp simp:inj_on_def image_def)
```
```   443
```
```   444 lemma fun_upd_image:
```
```   445      "f(x:=y) ` A = (if x \<in> A then insert y (f ` (A-{x})) else f ` A)"
```
```   446 by auto
```
```   447
```
```   448 lemma fun_upd_comp: "f \<circ> (g(x := y)) = (f \<circ> g)(x := f y)"
```
```   449 by (auto intro: ext)
```
```   450
```
```   451
```
```   452 subsection {* @{text override_on} *}
```
```   453
```
```   454 definition
```
```   455   override_on :: "('a \<Rightarrow> 'b) \<Rightarrow> ('a \<Rightarrow> 'b) \<Rightarrow> 'a set \<Rightarrow> 'a \<Rightarrow> 'b"
```
```   456 where
```
```   457   "override_on f g A = (\<lambda>a. if a \<in> A then g a else f a)"
```
```   458
```
```   459 lemma override_on_emptyset[simp]: "override_on f g {} = f"
```
```   460 by(simp add:override_on_def)
```
```   461
```
```   462 lemma override_on_apply_notin[simp]: "a ~: A ==> (override_on f g A) a = f a"
```
```   463 by(simp add:override_on_def)
```
```   464
```
```   465 lemma override_on_apply_in[simp]: "a : A ==> (override_on f g A) a = g a"
```
```   466 by(simp add:override_on_def)
```
```   467
```
```   468
```
```   469 subsection {* @{text swap} *}
```
```   470
```
```   471 definition
```
```   472   swap :: "'a \<Rightarrow> 'a \<Rightarrow> ('a \<Rightarrow> 'b) \<Rightarrow> ('a \<Rightarrow> 'b)"
```
```   473 where
```
```   474   "swap a b f = f (a := f b, b:= f a)"
```
```   475
```
```   476 lemma swap_self [simp]: "swap a a f = f"
```
```   477 by (simp add: swap_def)
```
```   478
```
```   479 lemma swap_commute: "swap a b f = swap b a f"
```
```   480 by (rule ext, simp add: fun_upd_def swap_def)
```
```   481
```
```   482 lemma swap_nilpotent [simp]: "swap a b (swap a b f) = f"
```
```   483 by (rule ext, simp add: fun_upd_def swap_def)
```
```   484
```
```   485 lemma swap_triple:
```
```   486   assumes "a \<noteq> c" and "b \<noteq> c"
```
```   487   shows "swap a b (swap b c (swap a b f)) = swap a c f"
```
```   488   using assms by (simp add: expand_fun_eq swap_def)
```
```   489
```
```   490 lemma comp_swap: "f \<circ> swap a b g = swap a b (f \<circ> g)"
```
```   491 by (rule ext, simp add: fun_upd_def swap_def)
```
```   492
```
```   493 lemma inj_on_imp_inj_on_swap:
```
```   494   "[|inj_on f A; a \<in> A; b \<in> A|] ==> inj_on (swap a b f) A"
```
```   495 by (simp add: inj_on_def swap_def, blast)
```
```   496
```
```   497 lemma inj_on_swap_iff [simp]:
```
```   498   assumes A: "a \<in> A" "b \<in> A" shows "inj_on (swap a b f) A = inj_on f A"
```
```   499 proof
```
```   500   assume "inj_on (swap a b f) A"
```
```   501   with A have "inj_on (swap a b (swap a b f)) A"
```
```   502     by (iprover intro: inj_on_imp_inj_on_swap)
```
```   503   thus "inj_on f A" by simp
```
```   504 next
```
```   505   assume "inj_on f A"
```
```   506   with A show "inj_on (swap a b f) A" by (iprover intro: inj_on_imp_inj_on_swap)
```
```   507 qed
```
```   508
```
```   509 lemma surj_imp_surj_swap: "surj f ==> surj (swap a b f)"
```
```   510 apply (simp add: surj_def swap_def, clarify)
```
```   511 apply (case_tac "y = f b", blast)
```
```   512 apply (case_tac "y = f a", auto)
```
```   513 done
```
```   514
```
```   515 lemma surj_swap_iff [simp]: "surj (swap a b f) = surj f"
```
```   516 proof
```
```   517   assume "surj (swap a b f)"
```
```   518   hence "surj (swap a b (swap a b f))" by (rule surj_imp_surj_swap)
```
```   519   thus "surj f" by simp
```
```   520 next
```
```   521   assume "surj f"
```
```   522   thus "surj (swap a b f)" by (rule surj_imp_surj_swap)
```
```   523 qed
```
```   524
```
```   525 lemma bij_swap_iff: "bij (swap a b f) = bij f"
```
```   526 by (simp add: bij_def)
```
```   527
```
```   528 hide (open) const swap
```
```   529
```
```   530
```
```   531 subsection {* Inversion of injective functions *}
```
```   532
```
```   533 definition the_inv_into :: "'a set => ('a => 'b) => ('b => 'a)" where
```
```   534 "the_inv_into A f == %x. THE y. y : A & f y = x"
```
```   535
```
```   536 lemma the_inv_into_f_f:
```
```   537   "[| inj_on f A;  x : A |] ==> the_inv_into A f (f x) = x"
```
```   538 apply (simp add: the_inv_into_def inj_on_def)
```
```   539 apply blast
```
```   540 done
```
```   541
```
```   542 lemma f_the_inv_into_f:
```
```   543   "inj_on f A ==> y : f`A  ==> f (the_inv_into A f y) = y"
```
```   544 apply (simp add: the_inv_into_def)
```
```   545 apply (rule the1I2)
```
```   546  apply(blast dest: inj_onD)
```
```   547 apply blast
```
```   548 done
```
```   549
```
```   550 lemma the_inv_into_into:
```
```   551   "[| inj_on f A; x : f ` A; A <= B |] ==> the_inv_into A f x : B"
```
```   552 apply (simp add: the_inv_into_def)
```
```   553 apply (rule the1I2)
```
```   554  apply(blast dest: inj_onD)
```
```   555 apply blast
```
```   556 done
```
```   557
```
```   558 lemma the_inv_into_onto[simp]:
```
```   559   "inj_on f A ==> the_inv_into A f ` (f ` A) = A"
```
```   560 by (fast intro:the_inv_into_into the_inv_into_f_f[symmetric])
```
```   561
```
```   562 lemma the_inv_into_f_eq:
```
```   563   "[| inj_on f A; f x = y; x : A |] ==> the_inv_into A f y = x"
```
```   564   apply (erule subst)
```
```   565   apply (erule the_inv_into_f_f, assumption)
```
```   566   done
```
```   567
```
```   568 lemma the_inv_into_comp:
```
```   569   "[| inj_on f (g ` A); inj_on g A; x : f ` g ` A |] ==>
```
```   570   the_inv_into A (f o g) x = (the_inv_into A g o the_inv_into (g ` A) f) x"
```
```   571 apply (rule the_inv_into_f_eq)
```
```   572   apply (fast intro: comp_inj_on)
```
```   573  apply (simp add: f_the_inv_into_f the_inv_into_into)
```
```   574 apply (simp add: the_inv_into_into)
```
```   575 done
```
```   576
```
```   577 lemma inj_on_the_inv_into:
```
```   578   "inj_on f A \<Longrightarrow> inj_on (the_inv_into A f) (f ` A)"
```
```   579 by (auto intro: inj_onI simp: image_def the_inv_into_f_f)
```
```   580
```
```   581 lemma bij_betw_the_inv_into:
```
```   582   "bij_betw f A B \<Longrightarrow> bij_betw (the_inv_into A f) B A"
```
```   583 by (auto simp add: bij_betw_def inj_on_the_inv_into the_inv_into_into)
```
```   584
```
```   585 abbreviation the_inv :: "('a \<Rightarrow> 'b) \<Rightarrow> ('b \<Rightarrow> 'a)" where
```
```   586   "the_inv f \<equiv> the_inv_into UNIV f"
```
```   587
```
```   588 lemma the_inv_f_f:
```
```   589   assumes "inj f"
```
```   590   shows "the_inv f (f x) = x" using assms UNIV_I
```
```   591   by (rule the_inv_into_f_f)
```
```   592
```
```   593
```
```   594 subsection {* Proof tool setup *}
```
```   595
```
```   596 text {* simplifies terms of the form
```
```   597   f(...,x:=y,...,x:=z,...) to f(...,x:=z,...) *}
```
```   598
```
```   599 simproc_setup fun_upd2 ("f(v := w, x := y)") = {* fn _ =>
```
```   600 let
```
```   601   fun gen_fun_upd NONE T _ _ = NONE
```
```   602     | gen_fun_upd (SOME f) T x y = SOME (Const (@{const_name fun_upd}, T) \$ f \$ x \$ y)
```
```   603   fun dest_fun_T1 (Type (_, T :: Ts)) = T
```
```   604   fun find_double (t as Const (@{const_name fun_upd},T) \$ f \$ x \$ y) =
```
```   605     let
```
```   606       fun find (Const (@{const_name fun_upd},T) \$ g \$ v \$ w) =
```
```   607             if v aconv x then SOME g else gen_fun_upd (find g) T v w
```
```   608         | find t = NONE
```
```   609     in (dest_fun_T1 T, gen_fun_upd (find f) T x y) end
```
```   610
```
```   611   fun proc ss ct =
```
```   612     let
```
```   613       val ctxt = Simplifier.the_context ss
```
```   614       val t = Thm.term_of ct
```
```   615     in
```
```   616       case find_double t of
```
```   617         (T, NONE) => NONE
```
```   618       | (T, SOME rhs) =>
```
```   619           SOME (Goal.prove ctxt [] [] (Logic.mk_equals (t, rhs))
```
```   620             (fn _ =>
```
```   621               rtac eq_reflection 1 THEN
```
```   622               rtac ext 1 THEN
```
```   623               simp_tac (Simplifier.inherit_context ss @{simpset}) 1))
```
```   624     end
```
```   625 in proc end
```
```   626 *}
```
```   627
```
```   628
```
```   629 subsection {* Code generator setup *}
```
```   630
```
```   631 types_code
```
```   632   "fun"  ("(_ ->/ _)")
```
```   633 attach (term_of) {*
```
```   634 fun term_of_fun_type _ aT _ bT _ = Free ("<function>", aT --> bT);
```
```   635 *}
```
```   636 attach (test) {*
```
```   637 fun gen_fun_type aF aT bG bT i =
```
```   638   let
```
```   639     val tab = Unsynchronized.ref [];
```
```   640     fun mk_upd (x, (_, y)) t = Const ("Fun.fun_upd",
```
```   641       (aT --> bT) --> aT --> bT --> aT --> bT) \$ t \$ aF x \$ y ()
```
```   642   in
```
```   643     (fn x =>
```
```   644        case AList.lookup op = (!tab) x of
```
```   645          NONE =>
```
```   646            let val p as (y, _) = bG i
```
```   647            in (tab := (x, p) :: !tab; y) end
```
```   648        | SOME (y, _) => y,
```
```   649      fn () => Basics.fold mk_upd (!tab) (Const ("HOL.undefined", aT --> bT)))
```
```   650   end;
```
```   651 *}
```
```   652
```
```   653 code_const "op \<circ>"
```
```   654   (SML infixl 5 "o")
```
```   655   (Haskell infixr 9 ".")
```
```   656
```
```   657 code_const "id"
```
```   658   (Haskell "id")
```
```   659
```
```   660 end
```