1 (**************************************************************************)
4 (* ||A|| A project by Andrea Asperti *)
6 (* ||I|| Developers: *)
7 (* ||T|| A.Asperti, C.Sacerdoti Coen, *)
8 (* ||A|| E.Tassi, S.Zacchiroli *)
10 (* \ / Matita is distributed under the terms of the *)
11 (* v GNU Lesser General Public License Version 2.1 *)
13 (**************************************************************************)
15 set "baseuri" "cic:/matita/nat/gcd".
17 include "nat/primes.ma".
18 include "higher_order_defs/functions.ma".
20 let rec gcd_aux p m n: nat \def
21 match divides_b n m with
26 |(S q) \Rightarrow gcd_aux q n (mod m n)]].
28 definition gcd : nat \to nat \to nat \def
34 | (S p) \Rightarrow gcd_aux (S p) m (S p) ]
38 | (S p) \Rightarrow gcd_aux (S p) n (S p) ]].
40 theorem divides_mod: \forall p,m,n:nat. O < n \to divides p m \to divides p n \to
42 intros.elim H1.elim H2.
43 apply witness ? ? (n2 - n1*(div m n)).
44 rewrite > distr_times_minus.
46 rewrite < assoc_times.
50 rewrite > div_mod m n in \vdash (? ? %).
52 apply eq_plus_to_le ? ? (mod m n).
55 apply div_mod.assumption. assumption.
58 theorem divides_mod_to_divides: \forall p,m,n:nat. O < n \to
59 divides p (mod m n) \to divides p n \to divides p m.
60 intros.elim H1.elim H2.
61 apply witness p m ((n1*(div m n))+n2).
62 rewrite > distr_times_plus.
64 rewrite < assoc_times.
65 rewrite < H4.rewrite < sym_times.
66 apply div_mod.assumption.
69 theorem divides_gcd_aux_mn: \forall p,m,n. O < n \to n \le m \to n \le p \to
70 divides (gcd_aux p m n) m \land divides (gcd_aux p m n) n.
72 absurd O < n.assumption.apply le_to_not_lt.assumption.
73 cut (divides n1 m) \lor \not (divides n1 m).
76 (match divides_b n1 m with
78 | false \Rightarrow gcd_aux n n1 (mod m n1)]) m) \land
80 (match divides_b n1 m with
82 | false \Rightarrow gcd_aux n n1 (mod m n1)]) n1).
83 elim Hcut.rewrite > divides_to_divides_b_true.
85 split.assumption.apply witness n1 n1 (S O).apply times_n_SO.
86 rewrite > not_divides_to_divides_b_false.
88 (divides (gcd_aux n n1 (mod m n1)) m) \land
89 (divides (gcd_aux n n1 (mod m n1)) n1).
90 cut (divides (gcd_aux n n1 (mod m n1)) n1) \land
91 (divides (gcd_aux n n1 (mod m n1)) (mod m n1)).
93 split.apply divides_mod_to_divides ? ? n1.
94 assumption.assumption.assumption.assumption.
96 cut O \lt mod m n1 \lor O = mod m n1.
97 elim Hcut1.assumption.
98 apply False_ind.apply H4.apply mod_O_to_divides.
99 assumption.apply sym_eq.assumption.
100 apply le_to_or_lt_eq.apply le_O_n.
102 apply lt_mod_m_m.assumption.
105 change with mod m n1 < n1.
106 apply lt_mod_m_m.assumption.assumption.
107 apply decidable_divides n1 m.assumption.
108 apply lt_to_le_to_lt ? n1.assumption.reflexivity.
110 assumption.assumption.
113 theorem divides_gcd_nm: \forall n,m.
114 divides (gcd n m) m \land divides (gcd n m) n.
122 | (S p) \Rightarrow gcd_aux (S p) m (S p) ]
126 | (S p) \Rightarrow gcd_aux (S p) n (S p) ]]) m
133 | (S p) \Rightarrow gcd_aux (S p) m (S p) ]
137 | (S p) \Rightarrow gcd_aux (S p) n (S p) ]]) n.
140 simplify.intros.split.
141 apply witness m m (S O).apply times_n_SO.
142 apply witness m O O.apply times_n_O.
144 divides (gcd_aux (S m1) m (S m1)) m
146 divides (gcd_aux (S m1) m (S m1)) (S m1).
147 apply divides_gcd_aux_mn.
148 simplify.apply le_S_S.apply le_O_n.
149 assumption.apply le_n.
152 simplify.intros.split.
153 apply witness n O O.apply times_n_O.
154 apply witness n n (S O).apply times_n_SO.
156 divides (gcd_aux (S m1) n (S m1)) (S m1)
158 divides (gcd_aux (S m1) n (S m1)) n.
159 cut divides (gcd_aux (S m1) n (S m1)) n
161 divides (gcd_aux (S m1) n (S m1)) (S m1).
162 elim Hcut.split.assumption.assumption.
163 apply divides_gcd_aux_mn.
164 simplify.apply le_S_S.apply le_O_n.
165 apply not_lt_to_le.simplify.intro.apply H.
166 rewrite > H1.apply trans_le ? (S n).
167 apply le_n_Sn.assumption.apply le_n.
170 theorem divides_gcd_n: \forall n,m.
173 exact proj2 ? ? (divides_gcd_nm n m).
176 theorem divides_gcd_m: \forall n,m.
179 exact proj1 ? ? (divides_gcd_nm n m).
182 theorem divides_gcd_aux: \forall p,m,n,d. O < n \to n \le m \to n \le p \to
183 divides d m \to divides d n \to divides d (gcd_aux p m n).
185 absurd O < n.assumption.apply le_to_not_lt.assumption.
188 (match divides_b n1 m with
189 [ true \Rightarrow n1
190 | false \Rightarrow gcd_aux n n1 (mod m n1)]).
191 cut divides n1 m \lor \not (divides n1 m).
193 rewrite > divides_to_divides_b_true.
195 rewrite > not_divides_to_divides_b_false.
196 change with divides d (gcd_aux n n1 (mod m n1)).
198 cut O \lt mod m n1 \lor O = mod m n1.
199 elim Hcut1.assumption.
200 absurd divides n1 m.apply mod_O_to_divides.
201 assumption.apply sym_eq.assumption.assumption.
202 apply le_to_or_lt_eq.apply le_O_n.
204 apply lt_mod_m_m.assumption.
207 change with mod m n1 < n1.
208 apply lt_mod_m_m.assumption.assumption.
210 apply divides_mod.assumption.assumption.assumption.
211 apply decidable_divides n1 m.assumption.
212 apply lt_to_le_to_lt ? n1.assumption.reflexivity.
213 assumption.assumption.assumption.
216 theorem divides_d_gcd: \forall m,n,d.
217 divides d m \to divides d n \to divides d (gcd n m).
225 | (S p) \Rightarrow gcd_aux (S p) m (S p) ]
229 | (S p) \Rightarrow gcd_aux (S p) n (S p) ]]).
231 apply nat_case1 n.simplify.intros.assumption.
233 change with divides d (gcd_aux (S m1) m (S m1)).
234 apply divides_gcd_aux.
235 simplify.apply le_S_S.apply le_O_n.assumption.apply le_n.assumption.
236 rewrite < H2.assumption.
237 apply nat_case1 m.simplify.intros.assumption.
239 change with divides d (gcd_aux (S m1) n (S m1)).
240 apply divides_gcd_aux.
241 simplify.apply le_S_S.apply le_O_n.
242 apply lt_to_le.apply not_le_to_lt.assumption.apply le_n.assumption.
243 rewrite < H2.assumption.
246 theorem eq_minus_gcd_aux: \forall p,m,n.O < n \to n \le m \to n \le p \to
247 ex nat (\lambda a. ex nat (\lambda b.
248 a*n - b*m = (gcd_aux p m n) \lor b*m - a*n = (gcd_aux p m n))).
251 absurd O < n.assumption.apply le_to_not_lt.assumption.
253 cut (divides n1 m) \lor \not (divides n1 m).
255 ex nat (\lambda a. ex nat (\lambda b.
256 a*n1 - b*m = match divides_b n1 m with
257 [ true \Rightarrow n1
258 | false \Rightarrow gcd_aux n n1 (mod m n1)]
260 b*m - a*n1 = match divides_b n1 m with
261 [ true \Rightarrow n1
262 | false \Rightarrow gcd_aux n n1 (mod m n1)])).
264 rewrite > divides_to_divides_b_true.
266 apply ex_intro ? ? (S O).
267 apply ex_intro ? ? O.
268 left.simplify.rewrite < plus_n_O.
269 apply sym_eq.apply minus_n_O.
270 rewrite > not_divides_to_divides_b_false.
272 ex nat (\lambda a. ex nat (\lambda b.
273 a*n1 - b*m = gcd_aux n n1 (mod m n1)
275 b*m - a*n1 = gcd_aux n n1 (mod m n1))).
277 ex nat (\lambda a. ex nat (\lambda b.
278 a*(mod m n1) - b*n1= gcd_aux n n1 (mod m n1)
280 b*n1 - a*(mod m n1) = gcd_aux n n1 (mod m n1))).
281 elim Hcut2.elim H5.elim H6.
284 apply ex_intro ? ? (a1+a*(div m n1)).
285 apply ex_intro ? ? a.
288 rewrite < sym_times n1.
289 rewrite > distr_times_plus.
290 rewrite > sym_times n1.
291 rewrite > sym_times n1.
292 rewrite > div_mod m n1 in \vdash (? ? (? % ?) ?).
293 rewrite > assoc_times.
295 rewrite > distr_times_plus.
296 rewrite < eq_minus_minus_minus_plus.
298 rewrite < plus_minus.
299 rewrite < minus_n_n.reflexivity.
302 apply ex_intro ? ? (a1+a*(div m n1)).
303 apply ex_intro ? ? a.
306 rewrite > distr_times_plus.
308 rewrite > sym_times n1.
309 rewrite > div_mod m n1 in \vdash (? ? (? ? %) ?).
310 rewrite > distr_times_plus.
311 rewrite > assoc_times.
312 rewrite < eq_minus_minus_minus_plus.
314 rewrite < plus_minus.
315 rewrite < minus_n_n.reflexivity.
316 (* end second case *)
317 apply H n1 (mod m n1).
318 (* a lot of trivialities left *)
319 cut O \lt mod m n1 \lor O = mod m n1.
320 elim Hcut2.assumption.
321 absurd divides n1 m.apply mod_O_to_divides.
322 assumption.apply sym_eq.assumption.assumption.
323 apply le_to_or_lt_eq.apply le_O_n.
325 apply lt_mod_m_m.assumption.
328 change with mod m n1 < n1.
329 apply lt_mod_m_m.assumption.assumption.
330 apply decidable_divides n1 m.assumption.
331 apply lt_to_le_to_lt ? n1.assumption.assumption.
332 assumption.assumption.assumption.assumption.assumption.
333 apply le_n.assumption.
337 theorem eq_minus_gcd: \forall m,n.
338 ex nat (\lambda a. ex nat (\lambda b.
339 a*n - b*m = (gcd n m) \lor b*m - a*n = (gcd n m))).
342 ex nat (\lambda a. ex nat (\lambda b.
348 | (S p) \Rightarrow gcd_aux (S p) m (S p) ]
352 | (S p) \Rightarrow gcd_aux (S p) n (S p) ]]
358 | (S p) \Rightarrow gcd_aux (S p) m (S p) ]
362 | (S p) \Rightarrow gcd_aux (S p) n (S p) ]]
367 apply ex_intro ? ? O.
368 apply ex_intro ? ? (S O).
371 apply sym_eq.apply minus_n_O.
374 ex nat (\lambda a. ex nat (\lambda b.
375 a*(S m1) - b*m = (gcd_aux (S m1) m (S m1))
376 \lor b*m - a*(S m1) = (gcd_aux (S m1) m (S m1)))).
377 apply eq_minus_gcd_aux.
378 simplify. apply le_S_S.apply le_O_n.
379 assumption.apply le_n.
382 apply ex_intro ? ? (S O).
383 apply ex_intro ? ? O.
386 apply sym_eq.apply minus_n_O.
389 ex nat (\lambda a. ex nat (\lambda b.
390 a*n - b*(S m1) = (gcd_aux (S m1) n (S m1))
391 \lor b*(S m1) - a*n = (gcd_aux (S m1) n (S m1)))).
393 ex nat (\lambda a. ex nat (\lambda b.
394 a*(S m1) - b*n = (gcd_aux (S m1) n (S m1))
396 b*n - a*(S m1) = (gcd_aux (S m1) n (S m1)))).
397 elim Hcut.elim H2.elim H3.
398 apply ex_intro ? ? a1.
399 apply ex_intro ? ? a.
401 apply ex_intro ? ? a1.
402 apply ex_intro ? ? a.
404 apply eq_minus_gcd_aux.
405 simplify. apply le_S_S.apply le_O_n.
406 apply lt_to_le.apply not_le_to_lt.assumption.
410 (* some properties of gcd *)
412 theorem gcd_O_n: \forall n:nat. gcd O n = n.
413 intro.simplify.reflexivity.
416 theorem gcd_O_to_eq_O:\forall m,n:nat. (gcd m n) = O \to
418 intros.cut divides O n \land divides O m.
419 elim Hcut.elim H2.split.
420 assumption.elim H1.assumption.
422 apply divides_gcd_nm.
425 theorem symmetric_gcd: symmetric nat gcd.
427 \forall n,m:nat. gcd n m = gcd m n.
429 cut O < (gcd n m) \lor O = (gcd n m).
431 cut O < (gcd m n) \lor O = (gcd m n).
434 apply divides_to_le.assumption.
435 apply divides_d_gcd.apply divides_gcd_n.apply divides_gcd_m.
436 apply divides_to_le.assumption.
437 apply divides_d_gcd.apply divides_gcd_n.apply divides_gcd_m.
440 elim Hcut2.rewrite > H2.rewrite > H3.reflexivity.
441 apply gcd_O_to_eq_O.apply sym_eq.assumption.
442 apply le_to_or_lt_eq.apply le_O_n.
445 elim Hcut1.rewrite > H1.rewrite > H2.reflexivity.
446 apply gcd_O_to_eq_O.apply sym_eq.assumption.
447 apply le_to_or_lt_eq.apply le_O_n.
450 variant sym_gcd: \forall n,m:nat. gcd n m = gcd m n \def
453 theorem gcd_SO_n: \forall n:nat. gcd (S O) n = (S O).
455 apply antisym_le.apply divides_to_le.simplify.apply le_n.
457 cut O < gcd (S O) n \lor O = gcd (S O) n.
458 elim Hcut.assumption.
461 cut (S O)=O \land n=O.
462 elim Hcut1.apply sym_eq.assumption.
463 apply gcd_O_to_eq_O.apply sym_eq.assumption.
464 apply le_to_or_lt_eq.apply le_O_n.
467 theorem prime_to_gcd_SO: \forall n,m:nat. prime n \to \not (divides n m) \to
469 intros.simplify in H.change with gcd n m = (S O).
473 change with (S (S O)) \le gcd n m \to False.intro.
474 apply H1.rewrite < H3 (gcd n m).
476 cut O < gcd n m \lor O = gcd n m.
477 elim Hcut.assumption.
479 apply not_le_Sn_O (S O).
481 elim Hcut1.rewrite < H5 in \vdash (? ? %).assumption.
482 apply gcd_O_to_eq_O.apply sym_eq.assumption.
483 apply le_to_or_lt_eq.apply le_O_n.
484 apply divides_gcd_n.assumption.
487 (* esempio di sfarfallalmento !!! *)
489 theorem bad: \forall n,p,q:nat.prime n \to divides n (p*q) \to
490 divides n p \lor divides n q.
492 cut divides n p \lor \not (divides n p).
493 elim Hcut.left.assumption.
495 cut ex nat (\lambda a. ex nat (\lambda b.
496 a*n - b*p = (S O) \lor b*p - a*n = (S O))).
497 elim Hcut1.elim H3.*)
499 theorem divides_times_to_divides: \forall n,p,q:nat.prime n \to divides n (p*q) \to
500 divides n p \lor divides n q.
502 cut divides n p \lor \not (divides n p).
506 cut ex nat (\lambda a. ex nat (\lambda b.
507 a*n - b*p = (S O) \lor b*p - a*n = (S O))).
508 elim Hcut1.elim H3.elim H4.
510 rewrite > times_n_SO q.rewrite < H5.
511 rewrite > distr_times_minus.
512 rewrite > sym_times q (a1*p).
513 rewrite > assoc_times a1.
514 elim H1.rewrite > H6.
515 rewrite < sym_times n.rewrite < assoc_times.
516 rewrite > sym_times q.rewrite > assoc_times.
517 rewrite < assoc_times a1.rewrite < sym_times n.
518 rewrite > assoc_times n.
519 rewrite < distr_times_minus.
520 apply witness ? ? (q*a-a1*n2).reflexivity.
522 rewrite > times_n_SO q.rewrite < H5.
523 rewrite > distr_times_minus.
524 rewrite > sym_times q (a1*p).
525 rewrite > assoc_times a1.
526 elim H1.rewrite > H6.
527 rewrite < sym_times.rewrite > assoc_times.
528 rewrite < assoc_times q.
529 rewrite < sym_times n.
530 rewrite < distr_times_minus.
531 apply witness ? ? (n2*a1-q*a).reflexivity.
532 (* end second case *)
533 rewrite < prime_to_gcd_SO n p.
535 apply decidable_divides n p.
536 apply trans_lt ? (S O).simplify.apply le_n.
537 simplify in H.elim H. assumption.
538 assumption.assumption.