X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=matita%2Fmatita%2Flib%2Fbasics%2Ftypes.ma;h=a5e35c9d218a5d756319dd429dd7e1b6d4e8363e;hb=376fd7774ef0fa2f30a4afb25aab6158e3cd04b7;hp=b7a022ad201056d7d5d1842ea9b3def64d0d862b;hpb=d2b59bd89f761a16a2dbc663f446b4f95c767b83;p=helm.git

diff --git a/matita/matita/lib/basics/types.ma b/matita/matita/lib/basics/types.ma
index b7a022ad2..a5e35c9d2 100644
--- a/matita/matita/lib/basics/types.ma
+++ b/matita/matita/lib/basics/types.ma
@@ -67,7 +67,7 @@ interpretation "mk_DPair" 'mk_DPair x y = (mk_DPair ?? x y).
 
 (* sigma *)
 record Sig (A:Type[0]) (f:A→Prop) : Type[0] ≝ {
-    pi1: A
+    pi1: A  (* not a coercion due to problems with Cerco *)
   ; pi2: f pi1
   }.
   
@@ -79,6 +79,9 @@ lemma sub_pi2 : ∀A.∀P,P':A → Prop. (∀x.P x → P' x) → ∀x:Σx:A.P x.
 #A #P #P' #H1 * #x #H2 @H1 @H2
 qed.
 
+lemma inj_mk_Sig: ∀A,P.∀x. x = mk_Sig A P (pi1 A P x) (pi2 A P x).
+#A #P #x cases x //
+qed-. 
 (* Prod *)
 
 record Prod (A,B:Type[0]) : Type[0] ≝ {