2 ||M|| This file is part of HELM, an Hypertextual, Electronic
3 ||A|| Library of Mathematics, developed at the Computer Science
4 ||T|| Department of the University of Bologna, Italy.
8 \ / This file is distributed under the terms of the
9 \ / GNU General Public License Version 2
10 V_____________________________________________________________*)
12 include "basics/vectors.ma".
13 (* include "basics/relations.ma". *)
15 (******************************** tape ****************************************)
17 (* A tape is essentially a triple 〈left,current,right〉 where however the current
18 symbol could be missing. This may happen for three different reasons: both tapes
19 are empty; we are on the left extremity of a non-empty tape (left overflow), or
20 we are on the right extremity of a non-empty tape (right overflow). *)
22 inductive tape (sig:FinSet) : Type[0] ≝
24 | leftof : sig → list sig → tape sig
25 | rightof : sig → list sig → tape sig
26 | midtape : list sig → sig → list sig → tape sig.
29 λsig.λt:tape sig.match t with
30 [ niltape ⇒ [] | leftof _ _ ⇒ [] | rightof s l ⇒ s::l | midtape l _ _ ⇒ l ].
33 λsig.λt:tape sig.match t with
34 [ niltape ⇒ [] | leftof s r ⇒ s::r | rightof _ _ ⇒ []| midtape _ _ r ⇒ r ].
37 λsig.λt:tape sig.match t with
38 [ midtape _ c _ ⇒ Some ? c | _ ⇒ None ? ].
41 ∀sig:FinSet.list sig → option sig → list sig → tape sig ≝
42 λsig,lt,c,rt.match c with
43 [ Some c' ⇒ midtape sig lt c' rt
44 | None ⇒ match lt with
47 | cons r0 rs0 ⇒ leftof ? r0 rs0 ]
48 | cons l0 ls0 ⇒ rightof ? l0 ls0 ] ].
50 inductive move : Type[0] ≝
51 | L : move | R : move | N : move.
53 (********************************** machine ***********************************)
55 record TM (sig:FinSet): Type[1] ≝
57 trans : states × (option sig) → states × (option (sig × move));
62 definition tape_move_left ≝ λsig:FinSet.λlt:list sig.λc:sig.λrt:list sig.
64 [ nil ⇒ leftof sig c rt
65 | cons c0 lt0 ⇒ midtape sig lt0 c0 (c::rt) ].
67 definition tape_move_right ≝ λsig:FinSet.λlt:list sig.λc:sig.λrt:list sig.
69 [ nil ⇒ rightof sig c lt
70 | cons c0 rt0 ⇒ midtape sig (c::lt) c0 rt0 ].
72 definition tape_move ≝ λsig.λt: tape sig.λm:option (sig × move).
78 [ R ⇒ tape_move_right ? (left ? t) s (right ? t)
79 | L ⇒ tape_move_left ? (left ? t) s (right ? t)
80 | N ⇒ midtape ? (left ? t) s (right ? t)
83 record config (sig,states:FinSet): Type[0] ≝
88 definition step ≝ λsig.λM:TM sig.λc:config sig (states sig M).
89 let current_char ≝ current ? (ctape ?? c) in
90 let 〈news,mv〉 ≝ trans sig M 〈cstate ?? c,current_char〉 in
91 mk_config ?? news (tape_move sig (ctape ?? c) mv).
93 (******************************** loop ****************************************)
94 let rec loop (A:Type[0]) n (f:A→A) p a on n ≝
97 | S m ⇒ if p a then (Some ? a) else loop A m f p (f a)
101 ∀A,n,f,p,a. p a = true →
102 loop A (S n) f p a = Some ? a.
103 #A #n #f #p #a #pa normalize >pa //
107 ∀A,n,f,p,a. p a = false →
108 loop A (S n) f p a = loop A n f p (f a).
109 normalize #A #n #f #p #a #Hpa >Hpa %
112 lemma loop_incr : ∀A,f,p,k1,k2,a1,a2.
113 loop A k1 f p a1 = Some ? a2 →
114 loop A (k2+k1) f p a1 = Some ? a2.
115 #A #f #p #k1 #k2 #a1 #a2 generalize in match a1; elim k1
116 [normalize #a0 #Hfalse destruct
117 |#k1' #IH #a0 <plus_n_Sm whd in ⊢ (??%? → ??%?);
118 cases (true_or_false (p a0)) #Hpa0 >Hpa0 whd in ⊢ (??%? → ??%?); // @IH
122 lemma loop_merge : ∀A,f,p,q.(∀b. p b = false → q b = false) →
124 loop A k1 f p a1 = Some ? a2 →
125 f a2 = a3 → q a2 = false →
126 loop A k2 f q a3 = Some ? a4 →
127 loop A (k1+k2) f q a1 = Some ? a4.
128 #Sig #f #p #q #Hpq #k1 elim k1
129 [normalize #k2 #a1 #a2 #a3 #a4 #H destruct
130 |#k1' #Hind #k2 #a1 #a2 #a3 #a4 normalize in ⊢ (%→?);
131 cases (true_or_false (p a1)) #pa1 >pa1 normalize in ⊢ (%→?);
132 [#eqa1a2 destruct #eqa2a3 #Hqa2 #H
133 whd in ⊢ (??(??%???)?); >plus_n_Sm @loop_incr
134 whd in ⊢ (??%?); >Hqa2 >eqa2a3 @H
135 |normalize >(Hpq … pa1) normalize #H1 #H2 #H3 @(Hind … H2) //
140 lemma loop_split : ∀A,f,p,q.(∀b. q b = true → p b = true) →
142 loop A k f q a1 = Some ? a2 →
144 loop A k1 f p a1 = Some ? a3 ∧
145 loop A (S(k-k1)) f q a3 = Some ? a2.
146 #A #f #p #q #Hpq #k elim k
147 [#a1 #a2 normalize #Heq destruct
148 |#i #Hind #a1 #a2 normalize
149 cases (true_or_false (q a1)) #Hqa1 >Hqa1 normalize
151 @(ex_intro … 1) @(ex_intro … a2) %
152 [normalize >(Hpq …Hqa1) // |>Hqa1 //]
153 |#Hloop cases (true_or_false (p a1)) #Hpa1
154 [@(ex_intro … 1) @(ex_intro … a1) %
155 [normalize >Hpa1 // |>Hqa1 <Hloop normalize //]
156 |cases (Hind …Hloop) #k2 * #a3 * #Hloop1 #Hloop2
157 @(ex_intro … (S k2)) @(ex_intro … a3) %
158 [normalize >Hpa1 normalize // | @Hloop2 ]
164 lemma loop_eq : ∀sig,f,q,i,j,a,x,y.
165 loop sig i f q a = Some ? x → loop sig j f q a = Some ? y → x = y.
166 #sig #f #q #i #j @(nat_elim2 … i j)
167 [ #n #a #x #y normalize #Hfalse destruct (Hfalse)
168 | #n #a #x #y #H1 normalize #Hfalse destruct (Hfalse)
169 | #n1 #n2 #IH #a #x #y normalize cases (q a) normalize
175 (************************** Realizability *************************************)
176 definition loopM ≝ λsig,M,i,cin.
177 loop ? i (step sig M) (λc.halt sig M (cstate ?? c)) cin.
179 definition initc ≝ λsig.λM:TM sig.λt.
180 mk_config sig (states sig M) (start sig M) t.
182 definition Realize ≝ λsig.λM:TM sig.λR:relation (tape sig).
184 loopM sig M i (initc sig M t) = Some ? outc ∧ R t (ctape ?? outc).
186 definition WRealize ≝ λsig.λM:TM sig.λR:relation (tape sig).
188 loopM sig M i (initc sig M t) = Some ? outc → R t (ctape ?? outc).
190 definition Terminate ≝ λsig.λM:TM sig.λt. ∃i,outc.
191 loopM sig M i (initc sig M t) = Some ? outc.
193 lemma WRealize_to_Realize : ∀sig.∀M: TM sig.∀R.
194 (∀t.Terminate sig M t) → WRealize sig M R → Realize sig M R.
195 #sig #M #R #HT #HW #t cases (HT … t) #i * #outc #Hloop
196 @(ex_intro … i) @(ex_intro … outc) % // @(HW … i) //
199 theorem Realize_to_WRealize : ∀sig,M,R.
200 Realize sig M R → WRealize sig M R.
201 #sig #M #R #H1 #inc #i #outc #Hloop
202 cases (H1 inc) #k * #outc1 * #Hloop1 #HR >(loop_eq … Hloop Hloop1) //
205 definition accRealize ≝ λsig.λM:TM sig.λacc:states sig M.λRtrue,Rfalse.
207 loopM sig M i (initc sig M t) = Some ? outc ∧
208 (cstate ?? outc = acc → Rtrue t (ctape ?? outc)) ∧
209 (cstate ?? outc ≠ acc → Rfalse t (ctape ?? outc)).
211 (******************************** NOP Machine *********************************)
216 definition nop_states ≝ initN 1.
217 definition start_nop : initN 1 ≝ mk_Sig ?? 0 (le_n … 1).
220 λalpha:FinSet.mk_TM alpha nop_states
221 (λp.let 〈q,a〉 ≝ p in 〈q,None ?〉)
224 definition R_nop ≝ λalpha.λt1,t2:tape alpha.t2 = t1.
227 ∀alpha.Realize alpha (nop alpha) (R_nop alpha).
228 #alpha #intape @(ex_intro ?? 1)
229 @(ex_intro … (mk_config ?? start_nop intape)) % %
232 (************************** Sequential Composition ****************************)
234 definition seq_trans ≝ λsig. λM1,M2 : TM sig.
238 if halt sig M1 s1 then 〈inr … (start sig M2), None ?〉
240 let 〈news1,m〉 ≝ trans sig M1 〈s1,a〉 in
243 let 〈news2,m〉 ≝ trans sig M2 〈s2,a〉 in
247 definition seq ≝ λsig. λM1,M2 : TM sig.
249 (FinSum (states sig M1) (states sig M2))
250 (seq_trans sig M1 M2)
251 (inl … (start sig M1))
253 [ inl _ ⇒ false | inr s2 ⇒ halt sig M2 s2]).
255 definition Rcomp ≝ λA.λR1,R2:relation A.λa1,a2.
256 ∃am.R1 a1 am ∧ R2 am a2.
258 interpretation "relation composition" 'compose R1 R2 = (Rcomp ? R1 R2).
260 definition lift_confL ≝
261 λsig,S1,S2,c.match c with
262 [ mk_config s t ⇒ mk_config sig (FinSum S1 S2) (inl … s) t ].
264 definition lift_confR ≝
265 λsig,S1,S2,c.match c with
266 [ mk_config s t ⇒ mk_config sig (FinSum S1 S2) (inr … s) t ].
268 definition halt_liftL ≝
269 λS1,S2,halt.λs:FinSum S1 S2.
272 | inr _ ⇒ true ]. (* should be vacuous in all cases we use halt_liftL *)
274 definition halt_liftR ≝
275 λS1,S2,halt.λs:FinSum S1 S2.
278 | inr s2 ⇒ halt s2 ].
280 lemma p_halt_liftL : ∀sig,S1,S2,halt,c.
281 halt (cstate sig S1 c) =
282 halt_liftL S1 S2 halt (cstate … (lift_confL … c)).
283 #sig #S1 #S2 #halt #c cases c #s #t %
286 lemma trans_liftL : ∀sig,M1,M2,s,a,news,move.
287 halt ? M1 s = false →
288 trans sig M1 〈s,a〉 = 〈news,move〉 →
289 trans sig (seq sig M1 M2) 〈inl … s,a〉 = 〈inl … news,move〉.
290 #sig (*#M1*) * #Q1 #T1 #init1 #halt1 #M2 #s #a #news #move
291 #Hhalt #Htrans whd in ⊢ (??%?); >Hhalt >Htrans %
294 lemma trans_liftR : ∀sig,M1,M2,s,a,news,move.
295 halt ? M2 s = false →
296 trans sig M2 〈s,a〉 = 〈news,move〉 →
297 trans sig (seq sig M1 M2) 〈inr … s,a〉 = 〈inr … news,move〉.
298 #sig #M1 * #Q2 #T2 #init2 #halt2 #s #a #news #move
299 #Hhalt #Htrans whd in ⊢ (??%?); >Hhalt >Htrans %
304 cstate sig M c1 = cstate sig M c2 →
305 ctape sig M c1 = ctape sig M c2 → c1 = c2.
306 #sig #M1 * #s1 #t1 * #s2 #t2 //
309 lemma step_lift_confR : ∀sig,M1,M2,c0.
310 halt ? M2 (cstate ?? c0) = false →
311 step sig (seq sig M1 M2) (lift_confR sig (states ? M1) (states ? M2) c0) =
312 lift_confR sig (states ? M1) (states ? M2) (step sig M2 c0).
313 #sig #M1 (* * #Q1 #T1 #init1 #halt1 *) #M2 * #s #t
314 lapply (refl ? (trans ?? 〈s,current sig t〉))
315 cases (trans ?? 〈s,current sig t〉) in ⊢ (???% → %);
318 | 2,3: #s1 #l1 #Heq #Hhalt
319 |#ls #s1 #rs #Heq #Hhalt ]
320 whd in ⊢ (???(????%)); >Heq
322 whd in ⊢ (??(???%)?); whd in ⊢ (??%?);
323 >(trans_liftR … Heq) //
326 lemma step_lift_confL : ∀sig,M1,M2,c0.
327 halt ? M1 (cstate ?? c0) = false →
328 step sig (seq sig M1 M2) (lift_confL sig (states ? M1) (states ? M2) c0) =
329 lift_confL sig ?? (step sig M1 c0).
330 #sig #M1 (* * #Q1 #T1 #init1 #halt1 *) #M2 * #s #t
331 lapply (refl ? (trans ?? 〈s,current sig t〉))
332 cases (trans ?? 〈s,current sig t〉) in ⊢ (???% → %);
335 | 2,3: #s1 #l1 #Heq #Hhalt
336 |#ls #s1 #rs #Heq #Hhalt ]
337 whd in ⊢ (???(????%)); >Heq
339 whd in ⊢ (??(???%)?); whd in ⊢ (??%?);
340 >(trans_liftL … Heq) //
343 lemma loop_lift : ∀A,B,k,lift,f,g,h,hlift,c1,c2.
344 (∀x.hlift (lift x) = h x) →
345 (∀x.h x = false → lift (f x) = g (lift x)) →
346 loop A k f h c1 = Some ? c2 →
347 loop B k g hlift (lift c1) = Some ? (lift … c2).
348 #A #B #k #lift #f #g #h #hlift #c1 #c2 #Hfg #Hhlift
349 generalize in match c1; elim k
350 [#c0 normalize in ⊢ (??%? → ?); #Hfalse destruct (Hfalse)
351 |#k0 #IH #c0 whd in ⊢ (??%? → ??%?);
352 cases (true_or_false (h c0)) #Hc0 >Hfg >Hc0
353 [ normalize #Heq destruct (Heq) %
354 | normalize <Hhlift // @IH ]
358 lemma loop_liftL : ∀sig,k,M1,M2,c1,c2.
359 loop ? k (step sig M1) (λc.halt sig M1 (cstate ?? c)) c1 = Some ? c2 →
360 loop ? k (step sig (seq sig M1 M2))
361 (λc.halt_liftL ?? (halt sig M1) (cstate ?? c)) (lift_confL … c1) =
362 Some ? (lift_confL … c2).
363 #sig #k #M1 #M2 #c1 #c2 generalize in match c1;
365 [#c0 normalize in ⊢ (??%? → ?); #Hfalse destruct (Hfalse)
366 |#k0 #IH #c0 whd in ⊢ (??%? → ??%?);
367 cases (true_or_false (halt ?? (cstate sig (states ? M1) c0))) #Hc0 >Hc0
368 [ >(?: halt_liftL ?? (halt sig M1) (cstate sig ? (lift_confL … c0)) = true)
369 [ whd in ⊢ (??%? → ??%?); #Hc2 destruct (Hc2) %
371 | >(?: halt_liftL ?? (halt sig M1) (cstate ?? (lift_confL … c0)) = false)
372 [whd in ⊢ (??%? → ??%?); #Hc2 <(IH ? Hc2) @eq_f
377 lemma loop_liftR : ∀sig,k,M1,M2,c1,c2.
378 loop ? k (step sig M2) (λc.halt sig M2 (cstate ?? c)) c1 = Some ? c2 →
379 loop ? k (step sig (seq sig M1 M2))
380 (λc.halt sig (seq sig M1 M2) (cstate ?? c)) (lift_confR … c1) =
381 Some ? (lift_confR … c2).
382 #sig #k #M1 #M2 #c1 #c2 generalize in match c1;
384 [#c0 normalize in ⊢ (??%? → ?); #Hfalse destruct (Hfalse)
385 |#k0 #IH #c0 whd in ⊢ (??%? → ??%?);
386 cases (true_or_false (halt ?? (cstate sig ? c0))) #Hc0 >Hc0
387 [ >(?: halt ? (seq sig M1 M2) (cstate sig ? (lift_confR … c0)) = true)
388 [ whd in ⊢ (??%? → ??%?); #Hc2 destruct (Hc2) %
390 | >(?: halt ? (seq sig M1 M2) (cstate sig ? (lift_confR … c0)) = false)
391 [whd in ⊢ (??%? → ??%?); #Hc2 <(IH ? Hc2) @eq_f
400 ∀A,k,f,p,a,b.loop A k f p a = Some ? b → p b = true.
402 [#a #b normalize #Hfalse destruct
403 |#k0 #IH #a #b whd in ⊢ (??%? → ?); cases (true_or_false (p a)) #Hpa
404 [ >Hpa normalize #H1 destruct //
410 lemma trans_liftL_true : ∀sig,M1,M2,s,a.
412 trans sig (seq sig M1 M2) 〈inl … s,a〉 = 〈inr … (start ? M2),None ?〉.
414 #Hhalt whd in ⊢ (??%?); >Hhalt %
417 lemma eq_ctape_lift_conf_L : ∀sig,S1,S2,outc.
418 ctape sig (FinSum S1 S2) (lift_confL … outc) = ctape … outc.
419 #sig #S1 #S2 #outc cases outc #s #t %
422 lemma eq_ctape_lift_conf_R : ∀sig,S1,S2,outc.
423 ctape sig (FinSum S1 S2) (lift_confR … outc) = ctape … outc.
424 #sig #S1 #S2 #outc cases outc #s #t %
427 theorem sem_seq: ∀sig,M1,M2,R1,R2.
428 Realize sig M1 R1 → Realize sig M2 R2 →
429 Realize sig (seq sig M1 M2) (R1 ∘ R2).
430 #sig #M1 #M2 #R1 #R2 #HR1 #HR2 #t
431 cases (HR1 t) #k1 * #outc1 * #Hloop1 #HM1
432 cases (HR2 (ctape sig (states ? M1) outc1)) #k2 * #outc2 * #Hloop2 #HM2
433 @(ex_intro … (k1+k2)) @(ex_intro … (lift_confR … outc2))
435 [@(loop_merge ???????????
436 (loop_lift ??? (lift_confL sig (states sig M1) (states sig M2))
437 (step sig M1) (step sig (seq sig M1 M2))
438 (λc.halt sig M1 (cstate … c))
439 (λc.halt_liftL ?? (halt sig M1) (cstate … c)) … Hloop1))
441 [ #sl #tl whd in ⊢ (??%? → ?); #Hl %
442 | #sr #tr whd in ⊢ (??%? → ?); #Hr destruct (Hr) ]
443 || #c0 #Hhalt <step_lift_confL //
445 |6:cases outc1 #s1 #t1 %
446 |7:@(loop_lift … (initc ?? (ctape … outc1)) … Hloop2)
448 | #c0 #Hhalt <step_lift_confR // ]
449 |whd in ⊢ (??(???%)?);whd in ⊢ (??%?);
450 generalize in match Hloop1; cases outc1 #sc1 #tc1 #Hloop10
451 >(trans_liftL_true sig M1 M2 ??)
452 [ whd in ⊢ (??%?); whd in ⊢ (???%);
453 @config_eq whd in ⊢ (???%); //
454 | @(loop_Some ?????? Hloop10) ]
456 | @(ex_intro … (ctape ? (FinSum (states ? M1) (states ? M2)) (lift_confL … outc1)))
457 % // >eq_ctape_lift_conf_L >eq_ctape_lift_conf_R //