src/HOL/Fun.ML

Improved error message.

(*  Title:      HOL/Fun
    ID:         $Id$
    Author:     Tobias Nipkow, Cambridge University Computer Laboratory
    Copyright   1993  University of Cambridge

Lemmas about functions.
*)

Goal "(f = g) = (! x. f(x)=g(x))";
by (rtac iffI 1);
by (Asm_simp_tac 1);
by (rtac ext 1 THEN Asm_simp_tac 1);
qed "expand_fun_eq";

val prems = Goal
    "[| f(x)=u;  !!x. P(x) ==> g(f(x)) = x;  P(x) |] ==> x=g(u)";
by (rtac (arg_cong RS box_equals) 1);
by (REPEAT (resolve_tac (prems@[refl]) 1));
qed "apply_inverse";


section "id";

Goalw [id_def] "id x = x";
by (rtac refl 1);
qed "id_apply";
Addsimps [id_apply];


section "o";

Goalw [o_def] "(f o g) x = f (g x)";
by (rtac refl 1);
qed "o_apply";
Addsimps [o_apply];

Goalw [o_def] "f o (g o h) = f o g o h";
by (rtac ext 1);
by (rtac refl 1);
qed "o_assoc";

Goalw [id_def] "id o g = g";
by (rtac ext 1);
by (Simp_tac 1);
qed "id_o";
Addsimps [id_o];

Goalw [id_def] "f o id = f";
by (rtac ext 1);
by (Simp_tac 1);
qed "o_id";
Addsimps [o_id];

Goalw [o_def] "(f o g)`r = f`(g`r)";
by (Blast_tac 1);
qed "image_compose";

Goal "f`A = (UN x:A. {f x})";
by (Blast_tac 1);
qed "image_eq_UN";

Goalw [o_def] "UNION A (g o f) = UNION (f`A) g";
by (Blast_tac 1);
qed "UN_o";

(** lemma for proving injectivity of representation functions for **)
(** datatypes involving function types                            **)

Goalw [o_def]
  "[| ! x y. g (f x) = g y --> f x = y; g o f = g o fa |] ==> f = fa";
by (rtac ext 1);
by (etac allE 1);
by (etac allE 1);
by (etac mp 1);
by (etac fun_cong 1);
qed "inj_fun_lemma";


section "inj";
(**NB: inj now just translates to inj_on**)

(*** inj(f): f is a one-to-one function ***)

(*for Tools/datatype_rep_proofs*)
val [prem] = Goalw [inj_on_def]
    "(!! x. ALL y. f(x) = f(y) --> x=y) ==> inj(f)";
by (blast_tac (claset() addIs [prem RS spec RS mp]) 1);
qed "datatype_injI";

Goalw [inj_on_def] "[| inj(f); f(x) = f(y) |] ==> x=y";
by (Blast_tac 1);
qed "injD";

(*Useful with the simplifier*)
Goal "inj(f) ==> (f(x) = f(y)) = (x=y)";
by (rtac iffI 1);
by (etac arg_cong 2);
by (etac injD 1);
by (assume_tac 1);
qed "inj_eq";

Goalw [o_def] "[| inj f; f o g = f o h |] ==> g = h";
by (rtac ext 1);
by (etac injD 1);
by (etac fun_cong 1);
qed "inj_o";

(*** inj_on f A: f is one-to-one over A ***)

val prems = Goalw [inj_on_def]
    "(!! x y. [|  x:A;  y:A;  f(x) = f(y) |] ==> x=y) ==> inj_on f A";
by (blast_tac (claset() addIs prems) 1);
qed "inj_onI";
bind_thm ("injI", inj_onI);                  (*for compatibility*)

val [major] = Goal 
    "(!!x. x:A ==> g(f(x)) = x) ==> inj_on f A";
by (rtac inj_onI 1);
by (etac (apply_inverse RS trans) 1);
by (REPEAT (eresolve_tac [asm_rl,major] 1));
qed "inj_on_inverseI";
bind_thm ("inj_inverseI", inj_on_inverseI);   (*for compatibility*)

Goalw [inj_on_def] "[| inj_on f A;  f(x)=f(y);  x:A;  y:A |] ==> x=y";
by (Blast_tac 1);
qed "inj_onD";

Goal "[| inj_on f A;  x:A;  y:A |] ==> (f(x)=f(y)) = (x=y)";
by (blast_tac (claset() addSDs [inj_onD]) 1);
qed "inj_on_iff";

Goalw [o_def, inj_on_def]
     "[| inj_on f A;  inj_on g (f`A) |] ==> inj_on (g o f) A";
by (Blast_tac 1);
qed "comp_inj_on";

Goalw [inj_on_def] "[| inj_on f A;  ~x=y;  x:A;  y:A |] ==> ~ f(x)=f(y)";
by (Blast_tac 1);
qed "inj_on_contraD";

Goal "inj (%s. {s})";
by (rtac injI 1);
by (etac singleton_inject 1);
qed "inj_singleton";

Goalw [inj_on_def] "[| A<=B; inj_on f B |] ==> inj_on f A";
by (Blast_tac 1);
qed "subset_inj_on";


(** surj **)

val [prem] = Goalw [surj_def] "(!! x. g(f x) = x) ==> surj g";
by (blast_tac (claset() addIs [prem RS sym]) 1);
qed "surjI";

Goalw [surj_def] "surj f ==> range f = UNIV";
by Auto_tac;
qed "surj_range";

Goalw [surj_def] "surj f ==> EX x. y = f x";
by (Blast_tac 1);
qed "surjD";

val [p1, p2] = Goal "surj f ==> (!!x. y = f x ==> C) ==> C";
by (cut_facts_tac [p1 RS surjD] 1);
by (etac exE 1);
by (rtac p2 1);
by (atac 1);
qed "surjE";

Goalw [o_def, surj_def] "[| surj f;  surj g |] ==> surj (g o f)";
by (Clarify_tac 1); 
by (dres_inst_tac [("x","y")] spec 1); 
by (Clarify_tac 1); 
by (dres_inst_tac [("x","x")] spec 1); 
by (Blast_tac 1); 
qed "comp_surj";


(** Bijections **)

Goalw [bij_def] "[| inj f; surj f |] ==> bij f";
by (Blast_tac 1);
qed "bijI";

Goalw [bij_def] "bij f ==> inj f";
by (Blast_tac 1);
qed "bij_is_inj";

Goalw [bij_def] "bij f ==> surj f";
by (Blast_tac 1);
qed "bij_is_surj";


(** We seem to need both the id-forms and the (%x. x) forms; the latter can
    arise by rewriting, while id may be used explicitly. **)

Goal "(%x. x) ` Y = Y";
by (Blast_tac 1);
qed "image_ident";

Goalw [id_def] "id ` Y = Y";
by (Blast_tac 1);
qed "image_id";
Addsimps [image_ident, image_id];

Goal "(%x. x) -` Y = Y";
by (Blast_tac 1);
qed "vimage_ident";

Goalw [id_def] "id -` A = A";
by Auto_tac;
qed "vimage_id";
Addsimps [vimage_ident, vimage_id];

Goal "f -` (f ` A) = {y. EX x:A. f x = f y}";
by (blast_tac (claset() addIs [sym]) 1);
qed "vimage_image_eq";

Goal "f ` (f -` A) <= A";
by (Blast_tac 1);
qed "image_vimage_subset";

Goal "f ` (f -` A) = A Int range f";
by (Blast_tac 1);
qed "image_vimage_eq";
Addsimps [image_vimage_eq];

Goal "surj f ==> f ` (f -` A) = A";
by (asm_simp_tac (simpset() addsimps [surj_range]) 1);
qed "surj_image_vimage_eq";

Goalw [inj_on_def] "inj f ==> f -` (f ` A) = A";
by (Blast_tac 1);
qed "inj_vimage_image_eq";

Goalw [surj_def] "surj f ==> f -` B <= A ==> B <= f ` A";
by (blast_tac (claset() addIs [sym]) 1);
qed "vimage_subsetD";

Goalw [inj_on_def] "inj f ==> B <= f ` A ==> f -` B <= A";
by (Blast_tac 1);
qed "vimage_subsetI";

Goalw [bij_def] "bij f ==> (f -` B <= A) = (B <= f ` A)";
by (blast_tac (claset() delrules [subsetI]
			addIs [vimage_subsetI, vimage_subsetD]) 1);
qed "vimage_subset_eq";

Goal "f`(A Int B) <= f`A Int f`B";
by (Blast_tac 1);
qed "image_Int_subset";

Goal "f`A - f`B <= f`(A - B)";
by (Blast_tac 1);
qed "image_diff_subset";

Goalw [inj_on_def]
   "[| inj_on f C;  A<=C;  B<=C |] ==> f`(A Int B) = f`A Int f`B";
by (Blast_tac 1);
qed "inj_on_image_Int";

Goalw [inj_on_def]
   "[| inj_on f C;  A<=C;  B<=C |] ==> f`(A-B) = f`A - f`B";
by (Blast_tac 1);
qed "inj_on_image_set_diff";

Goalw [inj_on_def] "inj f ==> f`(A Int B) = f`A Int f`B";
by (Blast_tac 1);
qed "image_Int";

Goalw [inj_on_def] "inj f ==> f`(A-B) = f`A - f`B";
by (Blast_tac 1);
qed "image_set_diff";

Goal "inj f ==> (f a : f`A) = (a : A)";
by (blast_tac (claset() addDs [injD]) 1);
qed "inj_image_mem_iff";

Goalw [inj_on_def] "inj f ==> (f`A <= f`B) = (A<=B)";
by (Blast_tac 1);
qed "inj_image_subset_iff";

Goal "inj f ==> (f`A = f`B) = (A = B)";
by (blast_tac (claset() addSEs [equalityE] addDs [injD]) 1);
qed "inj_image_eq_iff";

Goal  "(f ` (UNION A B)) = (UN x:A.(f ` (B x)))";
by (Blast_tac 1);
qed "image_UN";

(*injectivity's required.  Left-to-right inclusion holds even if A is empty*)
Goalw [inj_on_def]
   "[| inj_on f C;  ALL x:A. B x <= C;  j:A |] \
\   ==> f ` (INTER A B) = (INT x:A. f ` B x)";
by (Blast_tac 1);
qed "image_INT";

(*Compare with image_INT: no use of inj_on, and if f is surjective then
  it doesn't matter whether A is empty*)
Goalw [bij_def] "bij f ==> f ` (INTER A B) = (INT x:A. f ` B x)";
by (asm_full_simp_tac (simpset() addsimps [inj_on_def, surj_def]) 1);
by (Blast_tac 1);  
qed "bij_image_INT";

Goal "surj f ==> -(f`A) <= f`(-A)";
by (auto_tac (claset(), simpset() addsimps [surj_def]));  
qed "surj_Compl_image_subset";

Goal "inj f ==> f`(-A) <= -(f`A)";
by (auto_tac (claset(), simpset() addsimps [inj_on_def]));  
qed "inj_image_Compl_subset";

Goalw [bij_def] "bij f ==> f`(-A) = -(f`A)";
by (rtac equalityI 1); 
by (ALLGOALS (asm_simp_tac (simpset() addsimps [inj_image_Compl_subset, 
                                                surj_Compl_image_subset]))); 
qed "bij_image_Compl_eq";

val set_cs = claset() delrules [equalityI];


section "fun_upd";

Goalw [fun_upd_def] "(f(x:=y) = f) = (f x = y)";
by Safe_tac;
by (etac subst 1);
by (rtac ext 2);
by Auto_tac;
qed "fun_upd_idem_iff";

(* f x = y ==> f(x:=y) = f *)
bind_thm("fun_upd_idem", fun_upd_idem_iff RS iffD2);

(* f(x := f x) = f *)
AddIffs [refl RS fun_upd_idem];

Goal "(f(x:=y))z = (if z=x then y else f z)";
by (simp_tac (simpset() addsimps [fun_upd_def]) 1);
qed "fun_upd_apply";
Addsimps [fun_upd_apply];

(* fun_upd_apply supersedes these two,   but they are useful 
   if fun_upd_apply is intentionally removed from the simpset *)
Goal "(f(x:=y)) x = y";
by (Simp_tac 1);
qed "fun_upd_same";

Goal "z~=x ==> (f(x:=y)) z = f z";
by (Asm_simp_tac 1);
qed "fun_upd_other";

Goal "f(x:=y,x:=z) = f(x:=z)";
by (rtac ext 1);
by (Simp_tac 1);
qed "fun_upd_upd";
Addsimps [fun_upd_upd];

(* simplifies terms of the form f(...,x:=y,...,x:=z,...) to f(...,x:=z,...) *)
local 
  fun gen_fun_upd  None    T _ _ = None
  |   gen_fun_upd (Some f) T x y = Some (Const ("Fun.fun_upd",T) $ f $ x $ y)
  fun dest_fun_T1 (Type (_,T::Ts)) = T
  fun find_double (t as Const ("Fun.fun_upd",T) $ f $ x $ y) = let
      fun find         (Const ("Fun.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
  val ss = simpset ();
  val fun_upd_prover = K [rtac eq_reflection 1, rtac ext 1, 
                          simp_tac ss 1]
  fun mk_eq_cterm sg T l r = Thm.cterm_of sg (equals T $ l $ r)
in 
  val fun_upd2_simproc = Simplifier.mk_simproc "fun_upd2"
   [Thm.read_cterm (sign_of (the_context ())) ("f(v:=w,x:=y)", HOLogic.termT)]
   (fn sg => (K (fn t => case find_double t of (T,None)=> None | (T,Some rhs)=> 
       Some (prove_goalw_cterm [] (mk_eq_cterm sg T t rhs) fun_upd_prover))))
end;
Addsimprocs[fun_upd2_simproc];

Goal "a ~= c ==> (m(a:=b))(c:=d) = (m(c:=d))(a:=b)";
by (rtac ext 1);
by Auto_tac;
qed "fun_upd_twist";


(*** -> and Pi, by Florian Kammueller and LCP ***)

val prems = Goalw [Pi_def]
"[| !!x. x: A ==> f x: B x; !!x. x ~: A  ==> f(x) = arbitrary|] \
\    ==> f: Pi A B";
by (auto_tac (claset(), simpset() addsimps prems));
qed "Pi_I";

val prems = Goal 
"[| !!x. x: A ==> f x: B; !!x. x ~: A  ==> f(x) = arbitrary|] ==> f: A funcset B";
by (blast_tac (claset() addIs Pi_I::prems) 1);
qed "funcsetI";

Goalw [Pi_def] "[|f: Pi A B; x: A|] ==> f x: B x";
by Auto_tac;
qed "Pi_mem";

Goalw [Pi_def] "[|f: A funcset B; x: A|] ==> f x: B";
by Auto_tac;
qed "funcset_mem";

Goalw [Pi_def] "[|f: Pi A B; x~: A|] ==> f x = arbitrary";
by Auto_tac;
qed "apply_arb";

Goalw [Pi_def] "[| f: Pi A B; g: Pi A B; ! x: A. f x = g x |] ==> f = g";
by (rtac ext 1);
by Auto_tac;
bind_thm ("Pi_extensionality", ballI RSN (3, result()));


(*** compose ***)

Goalw [Pi_def, compose_def, restrict_def]
     "[| f: A funcset B; g: B funcset C |]==> compose A g f: A funcset C";
by Auto_tac;
qed "funcset_compose";

Goal "[| f: A funcset B; g: B funcset C; h: C funcset D |]\
\     ==> compose A h (compose A g f) = compose A (compose B h g) f";
by (res_inst_tac [("A","A")] Pi_extensionality 1);
by (blast_tac (claset() addIs [funcset_compose]) 1);
by (blast_tac (claset() addIs [funcset_compose]) 1);
by (rewrite_goals_tac [Pi_def, compose_def, restrict_def]);  
by Auto_tac;
qed "compose_assoc";

Goal "x : A ==> compose A g f x = g(f(x))";
by (asm_simp_tac (simpset() addsimps [compose_def, restrict_def]) 1);
qed "compose_eq";

Goal "[| f ` A = B; g ` B = C |] ==> compose A g f ` A = C";
by (auto_tac (claset(), simpset() addsimps [image_def, compose_eq]));
qed "surj_compose";

Goal "[| f ` A = B; inj_on f A; inj_on g B |] ==> inj_on (compose A g f) A";
by (auto_tac (claset(), simpset() addsimps [inj_on_def, compose_eq]));
qed "inj_on_compose";


(*** restrict / lam ***)

Goal "f`A <= B ==> (lam x: A. f x) : A funcset B";
by (auto_tac (claset(),
	      simpset() addsimps [restrict_def, Pi_def]));
qed "restrict_in_funcset";

val prems = Goalw [restrict_def, Pi_def]
     "(!!x. x: A ==> f x: B x) ==> (lam x: A. f x) : Pi A B";
by (asm_simp_tac (simpset() addsimps prems) 1);
qed "restrictI";

Goal "(lam y: A. f y) x = (if x : A then f x else arbitrary)";
by (asm_simp_tac (simpset() addsimps [restrict_def]) 1);
qed "restrict_apply";
Addsimps [restrict_apply];

val prems = Goal
    "(!!x. x: A ==> f x = g x) ==> (lam x: A. f x) = (lam x: A. g x)";
by (rtac ext 1);
by (auto_tac (claset(),
	      simpset() addsimps prems@[restrict_def, Pi_def]));
qed "restrict_ext";

Goalw [inj_on_def, restrict_def] "inj_on (restrict f A) A = inj_on f A";
by Auto_tac;
qed "inj_on_restrict_eq";


Goal "f : A funcset B ==> compose A (lam y:B. y) f = f";
by (rtac ext 1); 
by (auto_tac (claset(), simpset() addsimps [compose_def, Pi_def])); 
qed "Id_compose";

Goal "g : A funcset B ==> compose A g (lam x:A. x) = g";
by (rtac ext 1); 
by (auto_tac (claset(), simpset() addsimps [compose_def, Pi_def])); 
qed "compose_Id";


(*** Pi ***)

Goalw [Pi_def] "[| B(x) = {};  x: A |] ==> (PI x: A. B x) = {}";
by Auto_tac;
qed "Pi_eq_empty";

Goal "[| (PI x: A. B x) ~= {};  x: A |] ==> B(x) ~= {}";
by (blast_tac (HOL_cs addIs [Pi_eq_empty]) 1);
qed "Pi_total1";

Goal "Pi {} B = { %x. arbitrary }";
by (auto_tac (claset() addIs [ext], simpset() addsimps [Pi_def]));
qed "Pi_empty";

val [major] = Goalw [Pi_def] "(!!x. x: A ==> B x <= C x) ==> Pi A B <= Pi A C";
by (auto_tac (claset(),
	      simpset() addsimps [impOfSubs major]));
qed "Pi_mono";