X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=helm%2Fsoftware%2Fmatita%2Fcontribs%2Fng_assembly%2Fcommon%2Fnat_lemmas.ma;h=64eeb50f122f07b427be0003725cd2c1b136a6a9;hb=45f87a7044ccab3d8f1300bfc33ca93a6ad868cb;hp=4bfc4c11832366232bf43595a755b02d06a98a5d;hpb=38fccc2b774e493a94eedef76342b56079c0e694;p=helm.git

diff --git a/helm/software/matita/contribs/ng_assembly/common/nat_lemmas.ma b/helm/software/matita/contribs/ng_assembly/common/nat_lemmas.ma
index 4bfc4c118..64eeb50f1 100644
--- a/helm/software/matita/contribs/ng_assembly/common/nat_lemmas.ma
+++ b/helm/software/matita/contribs/ng_assembly/common/nat_lemmas.ma
@@ -51,26 +51,6 @@ nlemma nat_destruct_S_0 : ∀n:nat.S n = O → False.
  napply I.
 nqed.
 
-nlemma symmetric_eqnat : symmetricT nat bool eq_nat.
- nnormalize;
- #n1;
- nelim n1;
- ##[ ##1: #n2;
-          nelim n2;
-          nnormalize;
-          ##[ ##1: napply refl_eq
-          ##| ##2: #n3; #H; napply refl_eq
-          ##]
- ##| ##2: #n2; #H; #n3;
-          nnormalize;
-          ncases n3;
-          nnormalize;
-          ##[ ##1: napply refl_eq
-          ##| ##2: #n4; napply (H n4)
-          ##]
- ##]
-nqed.
-
 nlemma eq_to_eqnat : ∀n1,n2:nat.n1 = n2 → eq_nat n1 n2 = true.
  #n1;
  nelim n1;
@@ -88,7 +68,15 @@ nlemma eq_to_eqnat : ∀n1,n2:nat.n1 = n2 → eq_nat n1 n2 = true.
                    napply (H n4 (nat_destruct_S_S … H1))
           ##]
  ##]
-nqed. 
+nqed.
+
+nlemma neqnat_to_neq : ∀n1,n2:nat.(eq_nat n1 n2 = false → n1 ≠ n2).
+ #n1; #n2; #H;
+ napply (not_to_not (n1 = n2) (eq_nat n1 n2 = true) …);
+ ##[ ##1: napply (eq_to_eqnat n1 n2)
+ ##| ##2: napply (eqfalse_to_neqtrue … H)
+ ##]
+nqed.
 
 nlemma eqnat_to_eq : ∀n1,n2:nat.(eq_nat n1 n2 = true → n1 = n2).
  #n1;
@@ -110,6 +98,31 @@ nlemma eqnat_to_eq : ∀n1,n2:nat.(eq_nat n1 n2 = true → n1 = n2).
  ##]
 nqed.
 
+nlemma neq_to_neqnat : ∀n1,n2:nat.n1 ≠ n2 → eq_nat n1 n2 = false.
+ #n1; #n2; #H;
+ napply (neqtrue_to_eqfalse (eq_nat n1 n2));
+ napply (not_to_not (eq_nat n1 n2 = true) (n1 = n2) ? H);
+ napply (eqnat_to_eq n1 n2).
+nqed.
+
+nlemma decidable_nat : ∀x,y:nat.decidable (x = y).
+ #x; #y; nnormalize;
+ napply (or2_elim (eq_nat x y = true) (eq_nat x y = false) ? (decidable_bexpr ?));
+ ##[ ##1: #H; napply (or2_intro1 (x = y) (x ≠ y) (eqnat_to_eq … H))
+ ##| ##2: #H; napply (or2_intro2 (x = y) (x ≠ y) (neqnat_to_neq … H))
+ ##]
+nqed.
+
+nlemma symmetric_eqnat : symmetricT nat bool eq_nat.
+ #n1; #n2;
+ napply (or2_elim (n1 = n2) (n1 ≠ n2) ? (decidable_nat n1 n2));
+ ##[ ##1: #H; nrewrite > H; napply refl_eq
+ ##| ##2: #H; nrewrite > (neq_to_neqnat n1 n2 H);
+          napply (symmetric_eq ? (eq_nat n2 n1) false);
+          napply (neq_to_neqnat n2 n1 (symmetric_neq ? n1 n2 H))
+ ##]
+nqed.
+
 nlemma Sn_p_n_to_S_npn : ∀n1,n2.(S n1) + n2 = S (n1 + n2).
  #n1;
  nelim n1;