X-Git-Url: http://matita.cs.unibo.it/gitweb/?p=helm.git;a=blobdiff_plain;f=matita%2Flibrary%2Fnat%2Fchinese_reminder.ma;fp=matita%2Flibrary%2Fnat%2Fchinese_reminder.ma;h=2bf3bc59e0d95c00510e827371b9eac04a453d1e;hp=0000000000000000000000000000000000000000;hb=f61af501fb4608cc4fb062a0864c774e677f0d76;hpb=58ae1809c352e71e7b5530dc41e2bfc834e1aef1

diff --git a/matita/library/nat/chinese_reminder.ma b/matita/library/nat/chinese_reminder.ma
new file mode 100644
index 000000000..2bf3bc59e
--- /dev/null
+++ b/matita/library/nat/chinese_reminder.ma
@@ -0,0 +1,247 @@
+(**************************************************************************)
+(*       ___	                                                          *)
+(*      ||M||                                                             *)
+(*      ||A||       A project by Andrea Asperti                           *)
+(*      ||T||                                                             *)
+(*      ||I||       Developers:                                           *)
+(*      ||T||       A.Asperti, C.Sacerdoti Coen,                          *)
+(*      ||A||       E.Tassi, S.Zacchiroli                                 *)
+(*      \   /                                                             *)
+(*       \ /        This file is distributed under the terms of the       *)
+(*        v         GNU Lesser General Public License Version 2.1         *)
+(*                                                                        *)
+(**************************************************************************)
+
+include "nat/exp.ma".
+include "nat/gcd.ma".
+include "nat/permutation.ma".
+include "nat/congruence.ma".
+
+theorem and_congruent_congruent: \forall m,n,a,b:nat. O < n \to O < m \to 
+gcd n m = (S O) \to ex nat (\lambda x. congruent x a m \land congruent x b n).
+intros.
+cut (\exists c,d.c*n - d*m = (S O) \lor d*m - c*n = (S O)).
+elim Hcut.elim H3.elim H4.
+apply (ex_intro nat ? ((a+b*m)*a1*n-b*a2*m)).
+split.
+(* congruent to a *)
+cut (a1*n = a2*m + (S O)).
+rewrite > assoc_times.
+rewrite > Hcut1.
+rewrite < (sym_plus ? (a2*m)).
+rewrite > distr_times_plus.
+rewrite < times_n_SO.
+rewrite > assoc_plus.
+rewrite < assoc_times.
+rewrite < times_plus_l.
+rewrite > eq_minus_plus_plus_minus.
+rewrite < times_minus_l.
+rewrite > sym_plus.
+apply (eq_times_plus_to_congruent ? ? ? ((b+(a+b*m)*a2)-b*a2)).
+assumption.reflexivity.
+apply le_times_l.
+apply (trans_le ? ((a+b*m)*a2)).
+apply le_times_l.
+apply (trans_le ? (b*m)).
+rewrite > times_n_SO in \vdash (? % ?).
+apply le_times_r.assumption.
+apply le_plus_n.
+apply le_plus_n.
+apply minus_to_plus.
+apply lt_to_le.
+change with (O + a2*m < a1*n).
+apply lt_minus_to_plus.
+rewrite > H5.unfold lt.apply le_n.
+assumption.
+(* congruent to b *)
+cut (a2*m = a1*n - (S O)).
+rewrite > (assoc_times b a2).
+rewrite > Hcut1.
+rewrite > distr_times_minus.
+rewrite < assoc_times.
+rewrite < eq_plus_minus_minus_minus.
+rewrite < times_n_SO.
+rewrite < times_minus_l.
+rewrite < sym_plus.
+apply (eq_times_plus_to_congruent ? ? ? ((a+b*m)*a1-b*a1)).
+assumption.reflexivity.
+rewrite > assoc_times.
+apply le_times_r.
+apply (trans_le ? (a1*n - a2*m)).
+rewrite > H5.apply le_n.
+apply (le_minus_m ? (a2*m)).
+apply le_times_l.
+apply le_times_l.
+apply (trans_le ? (b*m)).
+rewrite > times_n_SO in \vdash (? % ?).
+apply le_times_r.assumption.
+apply le_plus_n.
+apply sym_eq. apply plus_to_minus.
+rewrite > sym_plus.
+apply minus_to_plus.
+apply lt_to_le.
+change with (O + a2*m < a1*n).
+apply lt_minus_to_plus.
+rewrite > H5.unfold lt.apply le_n.
+assumption.
+(* and now the symmetric case; the price to pay for working
+   in nat instead than Z *)
+apply (ex_intro nat ? ((b+a*n)*a2*m-a*a1*n)).
+split.
+(* congruent to a *)
+cut (a1*n = a2*m - (S O)).
+rewrite > (assoc_times a a1).
+rewrite > Hcut1.
+rewrite > distr_times_minus.
+rewrite < assoc_times.
+rewrite < eq_plus_minus_minus_minus.
+rewrite < times_n_SO.
+rewrite < times_minus_l.
+rewrite < sym_plus.
+apply (eq_times_plus_to_congruent ? ? ? ((b+a*n)*a2-a*a2)).
+assumption.reflexivity.
+rewrite > assoc_times.
+apply le_times_r.
+apply (trans_le ? (a2*m - a1*n)).
+rewrite > H5.apply le_n.
+apply (le_minus_m ? (a1*n)).
+rewrite > assoc_times.rewrite > assoc_times.
+apply le_times_l.
+apply (trans_le ? (a*n)).
+rewrite > times_n_SO in \vdash (? % ?).
+apply le_times_r.assumption.
+apply le_plus_n.
+apply sym_eq.apply plus_to_minus.
+rewrite > sym_plus.
+apply minus_to_plus.
+apply lt_to_le.
+change with (O + a1*n < a2*m).
+apply lt_minus_to_plus.
+rewrite > H5.unfold lt.apply le_n.
+assumption.
+(* congruent to a *)
+cut (a2*m = a1*n + (S O)).
+rewrite > assoc_times.
+rewrite > Hcut1.
+rewrite > (sym_plus (a1*n)).
+rewrite > distr_times_plus.
+rewrite < times_n_SO.
+rewrite < assoc_times.
+rewrite > assoc_plus.
+rewrite < times_plus_l.
+rewrite > eq_minus_plus_plus_minus.
+rewrite < times_minus_l.
+rewrite > sym_plus.
+apply (eq_times_plus_to_congruent ? ? ? ((a+(b+a*n)*a1)-a*a1)).
+assumption.reflexivity.
+apply le_times_l.
+apply (trans_le ? ((b+a*n)*a1)).
+apply le_times_l.
+apply (trans_le ? (a*n)).
+rewrite > times_n_SO in \vdash (? % ?).
+apply le_times_r.
+assumption.
+apply le_plus_n.
+apply le_plus_n.
+apply minus_to_plus.
+apply lt_to_le.
+change with (O + a1*n < a2*m).
+apply lt_minus_to_plus.
+rewrite > H5.unfold lt.apply le_n.
+assumption.
+(* proof of the cut *)
+rewrite < H2.
+apply eq_minus_gcd.
+qed.
+
+theorem and_congruent_congruent_lt: \forall m,n,a,b:nat. O < n \to O < m \to 
+gcd n m = (S O) \to 
+ex nat (\lambda x. (congruent x a m \land congruent x b n) \land
+ (x < m*n)).
+intros.elim (and_congruent_congruent m n a b).
+elim H3.
+apply (ex_intro ? ? (a1 \mod (m*n))).
+split.split.
+apply (transitive_congruent m ? a1).
+unfold congruent.
+apply sym_eq.
+change with (congruent a1 (a1 \mod (m*n)) m).
+rewrite < sym_times.
+apply congruent_n_mod_times.
+assumption.assumption.assumption.
+apply (transitive_congruent n ? a1).
+unfold congruent.
+apply sym_eq.
+change with (congruent a1 (a1 \mod (m*n)) n).
+apply congruent_n_mod_times.
+assumption.assumption.assumption.
+apply lt_mod_m_m.
+rewrite > (times_n_O O).
+apply lt_times.assumption.assumption.
+assumption.assumption.assumption.
+qed.
+
+definition cr_pair : nat \to nat \to nat \to nat \to nat \def
+\lambda n,m,a,b. 
+min (pred (n*m)) (\lambda x. andb (eqb (x \mod n) a) (eqb (x \mod m) b)).
+
+theorem cr_pair1: cr_pair (S (S O)) (S (S (S O))) O O = O.
+reflexivity.
+qed.
+
+theorem cr_pair2: cr_pair (S(S O)) (S(S(S O))) (S O) O = (S(S(S O))).
+simplify.
+reflexivity.
+qed.
+
+theorem cr_pair3: cr_pair (S(S O)) (S(S(S O))) (S O) (S(S O)) = (S(S(S(S(S O))))).
+reflexivity.
+qed.
+
+theorem cr_pair4: cr_pair (S(S(S(S(S O))))) (S(S(S(S(S(S(S O))))))) (S(S(S O))) (S(S O)) = 
+(S(S(S(S(S(S(S(S(S(S(S(S(S(S(S(S(S(S(S(S(S(S(S O))))))))))))))))))))))).
+reflexivity.
+qed.
+
+theorem mod_cr_pair : \forall m,n,a,b. a \lt m \to b \lt n \to 
+gcd n m = (S O) \to 
+(cr_pair m n a b) \mod m = a \land (cr_pair m n a b) \mod n = b.
+intros.
+cut (andb (eqb ((cr_pair m n a b) \mod m) a) 
+         (eqb ((cr_pair m n a b) \mod n) b) = true).
+generalize in match Hcut.
+apply andb_elim.
+apply eqb_elim.intro.
+rewrite > H3.
+simplify.
+intro.split.reflexivity.
+apply eqb_true_to_eq.assumption.
+intro.
+simplify.
+intro.apply False_ind.
+apply not_eq_true_false.apply sym_eq.assumption.
+apply (f_min_aux_true 
+(\lambda x. andb (eqb (x \mod m) a) (eqb (x \mod n) b)) (pred (m*n)) O).
+elim (and_congruent_congruent_lt m n a b).
+apply (ex_intro ? ? a1).split.split.
+apply le_O_n.
+elim H3.apply le_S_S_to_le.apply (trans_le ? (m*n)).
+assumption.apply (nat_case (m*n)).apply le_O_n.
+intro.
+rewrite < pred_Sn.
+rewrite < plus_n_O.apply le_n.
+elim H3.elim H4.
+apply andb_elim.
+cut (a1 \mod m = a).
+cut (a1 \mod n = b).
+rewrite > (eq_to_eqb_true ? ? Hcut).
+rewrite > (eq_to_eqb_true ? ? Hcut1).
+simplify.reflexivity.
+rewrite < (lt_to_eq_mod b n).assumption.
+assumption.
+rewrite < (lt_to_eq_mod a m).assumption.
+assumption.
+apply (le_to_lt_to_lt ? b).apply le_O_n.assumption.
+apply (le_to_lt_to_lt ? a).apply le_O_n.assumption.
+assumption.
+qed.
\ No newline at end of file