2 Author: Lawrence C Paulson, Cambridge University Computer Laboratory
3 Copyright 1993 University of Cambridge
6 header {* Constructive Type Theory *}
12 ML_file "~~/src/Provers/typedsimp.ML"
13 setup Pure_Thy.old_appl_syntax_setup
22 T :: "t" (*F is empty, T contains one element*)
28 rec :: "[i, i, [i,i]=>i] => i"
32 when :: "[i, i=>i, i=>i]=>i"
33 (*General Sum and Binary Product*)
37 split :: "[i, [i,i]=>i] =>i"
38 (*General Product and Function Space*)
39 Prod :: "[t, i=>t]=>t"
41 Plus :: "[t,t]=>t" (infixr "+" 40)
46 Type :: "t => prop" ("(_ type)" [10] 5)
47 Eqtype :: "[t,t]=>prop" ("(_ =/ _)" [10,10] 5)
48 Elem :: "[i, t]=>prop" ("(_ /: _)" [10,10] 5)
49 Eqelem :: "[i,i,t]=>prop" ("(_ =/ _ :/ _)" [10,10,10] 5)
50 Reduce :: "[i,i]=>prop" ("Reduce[_,_]")
54 lambda :: "(i => i) => i" (binder "lam " 10)
55 app :: "[i,i]=>i" (infixl "`" 60)
59 pair :: "[i,i]=>i" ("(1<_,/_>)")
62 "_PROD" :: "[idt,t,t]=>t" ("(3PROD _:_./ _)" 10)
63 "_SUM" :: "[idt,t,t]=>t" ("(3SUM _:_./ _)" 10)
65 "PROD x:A. B" == "CONST Prod(A, %x. B)"
66 "SUM x:A. B" == "CONST Sum(A, %x. B)"
69 Arrow :: "[t,t]=>t" (infixr "-->" 30) where
70 "A --> B == PROD _:A. B"
72 Times :: "[t,t]=>t" (infixr "*" 50) where
76 lambda (binder "\<lambda>\<lambda>" 10) and
77 Elem ("(_ /\<in> _)" [10,10] 5) and
78 Eqelem ("(2_ =/ _ \<in>/ _)" [10,10,10] 5) and
79 Arrow (infixr "\<longrightarrow>" 30) and
80 Times (infixr "\<times>" 50)
82 notation (HTML output)
83 lambda (binder "\<lambda>\<lambda>" 10) and
84 Elem ("(_ /\<in> _)" [10,10] 5) and
85 Eqelem ("(2_ =/ _ \<in>/ _)" [10,10,10] 5) and
86 Times (infixr "\<times>" 50)
89 "_PROD" :: "[idt,t,t] => t" ("(3\<Pi> _\<in>_./ _)" 10)
90 "_SUM" :: "[idt,t,t] => t" ("(3\<Sigma> _\<in>_./ _)" 10)
93 "_PROD" :: "[idt,t,t] => t" ("(3\<Pi> _\<in>_./ _)" 10)
94 "_SUM" :: "[idt,t,t] => t" ("(3\<Sigma> _\<in>_./ _)" 10)
96 (*Reduction: a weaker notion than equality; a hack for simplification.
97 Reduce[a,b] means either that a=b:A for some A or else that "a" and "b"
98 are textually identical.*)
100 (*does not verify a:A! Sound because only trans_red uses a Reduce premise
101 No new theorems can be proved about the standard judgements.*)
103 refl_red: "\<And>a. Reduce[a,a]" and
104 red_if_equal: "\<And>a b A. a = b : A ==> Reduce[a,b]" and
105 trans_red: "\<And>a b c A. [| a = b : A; Reduce[b,c] |] ==> a = c : A" and
109 refl_type: "\<And>A. A type ==> A = A" and
110 refl_elem: "\<And>a A. a : A ==> a = a : A" and
114 sym_type: "\<And>A B. A = B ==> B = A" and
115 sym_elem: "\<And>a b A. a = b : A ==> b = a : A" and
119 trans_type: "\<And>A B C. [| A = B; B = C |] ==> A = C" and
120 trans_elem: "\<And>a b c A. [| a = b : A; b = c : A |] ==> a = c : A" and
122 equal_types: "\<And>a A B. [| a : A; A = B |] ==> a : B" and
123 equal_typesL: "\<And>a b A B. [| a = b : A; A = B |] ==> a = b : B" and
127 subst_type: "\<And>a A B. [| a : A; !!z. z:A ==> B(z) type |] ==> B(a) type" and
128 subst_typeL: "\<And>a c A B D. [| a = c : A; !!z. z:A ==> B(z) = D(z) |] ==> B(a) = D(c)" and
130 subst_elem: "\<And>a b A B. [| a : A; !!z. z:A ==> b(z):B(z) |] ==> b(a):B(a)" and
132 "\<And>a b c d A B. [| a=c : A; !!z. z:A ==> b(z)=d(z) : B(z) |] ==> b(a)=d(c) : B(a)" and
135 (*The type N -- natural numbers*)
139 NI_succ: "\<And>a. a : N ==> succ(a) : N" and
140 NI_succL: "\<And>a b. a = b : N ==> succ(a) = succ(b) : N" and
143 "\<And>p a b C. [| p: N; a: C(0); !!u v. [| u: N; v: C(u) |] ==> b(u,v): C(succ(u)) |]
144 ==> rec(p, a, %u v. b(u,v)) : C(p)" and
147 "\<And>p q a b c d C. [| p = q : N; a = c : C(0);
148 !!u v. [| u: N; v: C(u) |] ==> b(u,v) = d(u,v): C(succ(u)) |]
149 ==> rec(p, a, %u v. b(u,v)) = rec(q,c,d) : C(p)" and
152 "\<And>a b C. [| a: C(0); !!u v. [| u: N; v: C(u) |] ==> b(u,v): C(succ(u)) |]
153 ==> rec(0, a, %u v. b(u,v)) = a : C(0)" and
156 "\<And>p a b C. [| p: N; a: C(0);
157 !!u v. [| u: N; v: C(u) |] ==> b(u,v): C(succ(u)) |] ==>
158 rec(succ(p), a, %u v. b(u,v)) = b(p, rec(p, a, %u v. b(u,v))) : C(succ(p))" and
160 (*The fourth Peano axiom. See page 91 of Martin-Lof's book*)
162 "\<And>a. [| a: N; 0 = succ(a) : N |] ==> 0: F" and
165 (*The Product of a family of types*)
167 ProdF: "\<And>A B. [| A type; !!x. x:A ==> B(x) type |] ==> PROD x:A. B(x) type" and
170 "\<And>A B C D. [| A = C; !!x. x:A ==> B(x) = D(x) |] ==>
171 PROD x:A. B(x) = PROD x:C. D(x)" and
174 "\<And>b A B. [| A type; !!x. x:A ==> b(x):B(x)|] ==> lam x. b(x) : PROD x:A. B(x)" and
177 "\<And>b c A B. [| A type; !!x. x:A ==> b(x) = c(x) : B(x)|] ==>
178 lam x. b(x) = lam x. c(x) : PROD x:A. B(x)" and
180 ProdE: "\<And>p a A B. [| p : PROD x:A. B(x); a : A |] ==> p`a : B(a)" and
181 ProdEL: "\<And>p q a b A B. [| p=q: PROD x:A. B(x); a=b : A |] ==> p`a = q`b : B(a)" and
184 "\<And>a b A B. [| a : A; !!x. x:A ==> b(x) : B(x)|] ==>
185 (lam x. b(x)) ` a = b(a) : B(a)" and
188 "\<And>p A B. p : PROD x:A. B(x) ==> (lam x. p`x) = p : PROD x:A. B(x)" and
191 (*The Sum of a family of types*)
193 SumF: "\<And>A B. [| A type; !!x. x:A ==> B(x) type |] ==> SUM x:A. B(x) type" and
195 "\<And>A B C D. [| A = C; !!x. x:A ==> B(x) = D(x) |] ==> SUM x:A. B(x) = SUM x:C. D(x)" and
197 SumI: "\<And>a b A B. [| a : A; b : B(a) |] ==> <a,b> : SUM x:A. B(x)" and
198 SumIL: "\<And>a b c d A B. [| a=c:A; b=d:B(a) |] ==> <a,b> = <c,d> : SUM x:A. B(x)" and
201 "\<And>p c A B C. [| p: SUM x:A. B(x); !!x y. [| x:A; y:B(x) |] ==> c(x,y): C(<x,y>) |]
202 ==> split(p, %x y. c(x,y)) : C(p)" and
205 "\<And>p q c d A B C. [| p=q : SUM x:A. B(x);
206 !!x y. [| x:A; y:B(x) |] ==> c(x,y)=d(x,y): C(<x,y>)|]
207 ==> split(p, %x y. c(x,y)) = split(q, % x y. d(x,y)) : C(p)" and
210 "\<And>a b c A B C. [| a: A; b: B(a); !!x y. [| x:A; y:B(x) |] ==> c(x,y): C(<x,y>) |]
211 ==> split(<a,b>, %x y. c(x,y)) = c(a,b) : C(<a,b>)" and
213 fst_def: "\<And>a. fst(a) == split(a, %x y. x)" and
214 snd_def: "\<And>a. snd(a) == split(a, %x y. y)" and
217 (*The sum of two types*)
219 PlusF: "\<And>A B. [| A type; B type |] ==> A+B type" and
220 PlusFL: "\<And>A B C D. [| A = C; B = D |] ==> A+B = C+D" and
222 PlusI_inl: "\<And>a A B. [| a : A; B type |] ==> inl(a) : A+B" and
223 PlusI_inlL: "\<And>a c A B. [| a = c : A; B type |] ==> inl(a) = inl(c) : A+B" and
225 PlusI_inr: "\<And>b A B. [| A type; b : B |] ==> inr(b) : A+B" and
226 PlusI_inrL: "\<And>b d A B. [| A type; b = d : B |] ==> inr(b) = inr(d) : A+B" and
229 "\<And>p c d A B C. [| p: A+B; !!x. x:A ==> c(x): C(inl(x));
230 !!y. y:B ==> d(y): C(inr(y)) |]
231 ==> when(p, %x. c(x), %y. d(y)) : C(p)" and
234 "\<And>p q c d e f A B C. [| p = q : A+B; !!x. x: A ==> c(x) = e(x) : C(inl(x));
235 !!y. y: B ==> d(y) = f(y) : C(inr(y)) |]
236 ==> when(p, %x. c(x), %y. d(y)) = when(q, %x. e(x), %y. f(y)) : C(p)" and
239 "\<And>a c d A C. [| a: A; !!x. x:A ==> c(x): C(inl(x));
240 !!y. y:B ==> d(y): C(inr(y)) |]
241 ==> when(inl(a), %x. c(x), %y. d(y)) = c(a) : C(inl(a))" and
244 "\<And>b c d A B C. [| b: B; !!x. x:A ==> c(x): C(inl(x));
245 !!y. y:B ==> d(y): C(inr(y)) |]
246 ==> when(inr(b), %x. c(x), %y. d(y)) = d(b) : C(inr(b))" and
251 EqF: "\<And>a b A. [| A type; a : A; b : A |] ==> Eq(A,a,b) type" and
252 EqFL: "\<And>a b c d A B. [| A=B; a=c: A; b=d : A |] ==> Eq(A,a,b) = Eq(B,c,d)" and
253 EqI: "\<And>a b A. a = b : A ==> eq : Eq(A,a,b)" and
254 EqE: "\<And>p a b A. p : Eq(A,a,b) ==> a = b : A" and
256 (*By equality of types, can prove C(p) from C(eq), an elimination rule*)
257 EqC: "\<And>p a b A. p : Eq(A,a,b) ==> p = eq : Eq(A,a,b)" and
262 FE: "\<And>p C. [| p: F; C type |] ==> contr(p) : C" and
263 FEL: "\<And>p q C. [| p = q : F; C type |] ==> contr(p) = contr(q) : C" and
266 Martin-Lof's book (page 68) discusses elimination and computation.
267 Elimination can be derived by computation and equality of types,
268 but with an extra premise C(x) type x:T.
269 Also computation can be derived from elimination. *)
273 TE: "\<And>p c C. [| p : T; c : C(tt) |] ==> c : C(p)" and
274 TEL: "\<And>p q c d C. [| p = q : T; c = d : C(tt) |] ==> c = d : C(p)" and
275 TC: "\<And>p. p : T ==> p = tt : T"
278 subsection "Tactics and derived rules for Constructive Type Theory"
281 lemmas form_rls = NF ProdF SumF PlusF EqF FF TF
282 and formL_rls = ProdFL SumFL PlusFL EqFL
285 OMITTED: EqI, because its premise is an eqelem, not an elem*)
286 lemmas intr_rls = NI0 NI_succ ProdI SumI PlusI_inl PlusI_inr TI
287 and intrL_rls = NI_succL ProdIL SumIL PlusI_inlL PlusI_inrL
290 OMITTED: EqE, because its conclusion is an eqelem, not an elem
291 TE, because it does not involve a constructor *)
292 lemmas elim_rls = NE ProdE SumE PlusE FE
293 and elimL_rls = NEL ProdEL SumEL PlusEL FEL
295 (*OMITTED: eqC are TC because they make rewriting loop: p = un = un = ... *)
296 lemmas comp_rls = NC0 NC_succ ProdC SumC PlusC_inl PlusC_inr
298 (*rules with conclusion a:A, an elem judgement*)
299 lemmas element_rls = intr_rls elim_rls
301 (*Definitions are (meta)equality axioms*)
302 lemmas basic_defs = fst_def snd_def
304 (*Compare with standard version: B is applied to UNSIMPLIFIED expression! *)
305 lemma SumIL2: "[| c=a : A; d=b : B(a) |] ==> <c,d> = <a,b> : Sum(A,B)"
306 apply (rule sym_elem)
308 apply (rule_tac [!] sym_elem)
312 lemmas intrL2_rls = NI_succL ProdIL SumIL2 PlusI_inlL PlusI_inrL
314 (*Exploit p:Prod(A,B) to create the assumption z:B(a).
315 A more natural form of product elimination. *)
317 assumes "p: Prod(A,B)"
319 and "!!z. z: B(a) ==> c(z): C(z)"
320 shows "c(p`a): C(p`a)"
321 apply (rule assms ProdE)+
325 subsection {* Tactics for type checking *}
331 fun is_rigid_elem (Const("CTT.Elem",_) $ a $ _) = not(is_Var (head_of a))
332 | is_rigid_elem (Const("CTT.Eqelem",_) $ a $ _ $ _) = not(is_Var (head_of a))
333 | is_rigid_elem (Const("CTT.Type",_) $ a) = not(is_Var (head_of a))
334 | is_rigid_elem _ = false
338 (*Try solving a:A or a=b:A by assumption provided a is rigid!*)
339 val test_assume_tac = SUBGOAL(fn (prem,i) =>
340 if is_rigid_elem (Logic.strip_assums_concl prem)
341 then assume_tac i else no_tac)
343 fun ASSUME tf i = test_assume_tac i ORELSE tf i
349 (*For simplification: type formation and checking,
350 but no equalities between terms*)
351 lemmas routine_rls = form_rls formL_rls refl_type element_rls
355 val equal_rls = @{thms form_rls} @ @{thms element_rls} @ @{thms intrL_rls} @
356 @{thms elimL_rls} @ @{thms refl_elem}
359 fun routine_tac rls prems = ASSUME (filt_resolve_tac (prems @ rls) 4);
361 (*Solve all subgoals "A type" using formation rules. *)
362 val form_tac = REPEAT_FIRST (ASSUME (filt_resolve_tac @{thms form_rls} 1));
364 (*Type checking: solve a:A (a rigid, A flexible) by intro and elim rules. *)
365 fun typechk_tac thms =
366 let val tac = filt_resolve_tac (thms @ @{thms form_rls} @ @{thms element_rls}) 3
367 in REPEAT_FIRST (ASSUME tac) end
369 (*Solve a:A (a flexible, A rigid) by introduction rules.
370 Cannot use stringtrees (filt_resolve_tac) since
371 goals like ?a:SUM(A,B) have a trivial head-string *)
373 let val tac = filt_resolve_tac(thms @ @{thms form_rls} @ @{thms intr_rls}) 1
374 in REPEAT_FIRST (ASSUME tac) end
376 (*Equality proving: solve a=b:A (where a is rigid) by long rules. *)
378 REPEAT_FIRST (ASSUME (filt_resolve_tac (thms @ equal_rls) 3))
385 subsection {* Simplification *}
387 (*To simplify the type in a goal*)
388 lemma replace_type: "[| B = A; a : A |] ==> a : B"
389 apply (rule equal_types)
390 apply (rule_tac [2] sym_type)
394 (*Simplify the parameter of a unary type operator.*)
395 lemma subst_eqtyparg:
397 and 2: "!!z. z:A ==> B(z) type"
399 apply (rule subst_typeL)
400 apply (rule_tac [2] refl_type)
405 (*Simplification rules for Constructive Type Theory*)
406 lemmas reduction_rls = comp_rls [THEN trans_elem]
409 (*Converts each goal "e : Eq(A,a,b)" into "a=b:A" for simplification.
410 Uses other intro rules to avoid changing flexible goals.*)
411 val eqintr_tac = REPEAT_FIRST (ASSUME (filt_resolve_tac (@{thm EqI} :: @{thms intr_rls}) 1))
413 (** Tactics that instantiate CTT-rules.
414 Vars in the given terms will be incremented!
415 The (rtac EqE i) lets them apply to equality judgements. **)
417 fun NE_tac ctxt sp i =
418 TRY (rtac @{thm EqE} i) THEN res_inst_tac ctxt [(("p", 0), sp)] @{thm NE} i
420 fun SumE_tac ctxt sp i =
421 TRY (rtac @{thm EqE} i) THEN res_inst_tac ctxt [(("p", 0), sp)] @{thm SumE} i
423 fun PlusE_tac ctxt sp i =
424 TRY (rtac @{thm EqE} i) THEN res_inst_tac ctxt [(("p", 0), sp)] @{thm PlusE} i
426 (** Predicate logic reasoning, WITH THINNING!! Procedures adapted from NJ. **)
428 (*Finds f:Prod(A,B) and a:A in the assumptions, concludes there is z:B(a) *)
430 rtac @{thm subst_prodE} i THEN assume_tac i THEN assume_tac i
432 (*Finds P-->Q and P in the assumptions, replaces implication by Q *)
433 fun mp_tac i = etac @{thm subst_prodE} i THEN assume_tac i
435 (*"safe" when regarded as predicate calculus rules*)
436 val safe_brls = sort (make_ord lessb)
437 [ (true, @{thm FE}), (true,asm_rl),
438 (false, @{thm ProdI}), (true, @{thm SumE}), (true, @{thm PlusE}) ]
441 [ (false, @{thm PlusI_inl}), (false, @{thm PlusI_inr}), (false, @{thm SumI}),
442 (true, @{thm subst_prodE}) ]
444 (*0 subgoals vs 1 or more*)
445 val (safe0_brls, safep_brls) =
446 List.partition (curry (op =) 0 o subgoals_of_brl) safe_brls
448 fun safestep_tac thms i =
450 resolve_tac thms i ORELSE
451 biresolve_tac safe0_brls i ORELSE mp_tac i ORELSE
452 DETERM (biresolve_tac safep_brls i)
454 fun safe_tac thms i = DEPTH_SOLVE_1 (safestep_tac thms i)
456 fun step_tac thms = safestep_tac thms ORELSE' biresolve_tac unsafe_brls
458 (*Fails unless it solves the goal!*)
459 fun pc_tac thms = DEPTH_SOLVE_1 o (step_tac thms)
465 subsection {* The elimination rules for fst/snd *}
467 lemma SumE_fst: "p : Sum(A,B) ==> fst(p) : A"
468 apply (unfold basic_defs)
473 (*The first premise must be p:Sum(A,B) !!*)
475 assumes major: "p: Sum(A,B)"
477 and "!!x. x:A ==> B(x) type"
478 shows "snd(p) : B(fst(p))"
479 apply (unfold basic_defs)
480 apply (rule major [THEN SumE])
481 apply (rule SumC [THEN subst_eqtyparg, THEN replace_type])
482 apply (tactic {* typechk_tac @{thms assms} *})