X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=matita%2Fmatita%2Fcontribs%2Flambdadelta%2Fground_2%2Fynat%2Fynat.ma;h=7e2c2dc6c1a1211d4c4920cb02a590a8e2e589e8;hb=2601d0c1a860fdd08c4c1d71473917aa85eeb63a;hp=3dbc0c662b11c6465346474c53e3e2787ce82720;hpb=dd453d40e15929d6faef02f7b01a17f0cd6fc5b7;p=helm.git

diff --git a/matita/matita/contribs/lambdadelta/ground_2/ynat/ynat.ma b/matita/matita/contribs/lambdadelta/ground_2/ynat/ynat.ma
index 3dbc0c662..7e2c2dc6c 100644
--- a/matita/matita/contribs/lambdadelta/ground_2/ynat/ynat.ma
+++ b/matita/matita/contribs/lambdadelta/ground_2/ynat/ynat.ma
@@ -12,7 +12,7 @@
 (*                                                                        *)
 (**************************************************************************)
 
-include "arithmetics/nat.ma".
+include "ground_2/lib/arith.ma".
 include "ground_2/notation/constructors/infinity_0.ma".
 
 (* NATURAL NUMBERS WITH INFINITY ********************************************)
@@ -32,3 +32,11 @@ interpretation "ynat infinity" 'Infinity = Y.
 lemma yinj_inj: ∀m,n. yinj m = yinj n → m = n.
 #m #n #H destruct //
 qed-.
+
+(* Basic properties *********************************************************)
+
+lemma eq_ynat_dec: ∀n1,n2:ynat. Decidable (n1 = n2).
+* [ #n1 ] * [1,3: #n2 ] /2 width=1 by or_introl/
+[2,3: @or_intror #H destruct ]
+elim (eq_nat_dec n1 n2) /4 width=1 by yinj_inj, or_intror, or_introl/
+qed-.