AMBDA-TYPES: some improvements. subst now fully exploited

[helm.git] / matita / contribs / LAMBDA-TYPES / Base-1 / preamble.ma

diff --git a/matita/contribs/LAMBDA-TYPES/Base-1/preamble.ma b/matita/contribs/LAMBDA-TYPES/Base-1/preamble.ma
index 1a6874e54204330e3d60c22fa9157d031ad072fc..288e0626d82cf7545b9cb3e277d21c614264ee5e 100644 (file)
--- a/matita/contribs/LAMBDA-TYPES/Base-1/preamble.ma
+++ b/matita/contribs/LAMBDA-TYPES/Base-1/preamble.ma
@@ -97,6 +97,10 @@ theorem sym_not_eq: \forall A:Type. \forall x,y:A. x \neq y \to y \neq x.
  unfold not. intros. apply H. symmetry. assumption.
 qed.
 
+theorem trans_eq : \forall A:Type. \forall x,y,z:A. x=y \to y=z \to x=z.
+ intros. transitivity y; assumption.
+qed.
+
 theorem plus_reg_l: \forall n,m,p. n + m = n + p \to m = p.
  intros. apply plus_reg_l; auto.
 qed.