New theorem: eq_ind_r.

diff --git a/helm/matita/library/equality.ma b/helm/matita/library/equality.ma
index c49475c139ade0f1761df7e49095f25f41a2b3ec..cf513734aa07f7e40e6fa35604e2f01c8c84bf8b 100644 (file)
--- a/helm/matita/library/equality.ma
+++ b/helm/matita/library/equality.ma
@@ -26,6 +26,13 @@ theorem trans_eq : \forall A:Type.
 intros.elim H1.assumption.
 qed.
 
+theorem eq_ind_r :
+ \forall A:Type.\forall x:A. \forall P: A \to Prop.
+   P x \to \forall y:A. eq A y x \to P y.
+intros.letin H1' \def sym_eq ? ? ? H1.clearbody H1'.
+elim H1'.assumption.
+qed.
+
 theorem f_equal: \forall  A,B:Type.\forall f:A\to B.
 \forall x,y:A. eq A x y \to eq B (f x) (f y).
 intros.elim H.apply refl_equal.