X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=matita%2Fmatita%2Fcontribs%2Flambda_delta%2FGround_2%2Fstar.ma;h=e438b44f0c6bea578f1b243f7985aa68a8f51ec6;hb=aec661d51ffa04b4248cdfece772b58780737e3f;hp=e68ab1785666d895c110d1f0eddfdcf188d67d3c;hpb=f75be90562ddd964ef7ed43b956eb908f3133e3a;p=helm.git

diff --git a/matita/matita/contribs/lambda_delta/Ground_2/star.ma b/matita/matita/contribs/lambda_delta/Ground_2/star.ma
index e68ab1785..e438b44f0 100644
--- a/matita/matita/contribs/lambda_delta/Ground_2/star.ma
+++ b/matita/matita/contribs/lambda_delta/Ground_2/star.ma
@@ -17,6 +17,9 @@ include "Ground_2/xoa_props.ma".
 
 (* PROPERTIES of RELATIONS **************************************************)
 
+definition Decidable: Prop → Prop ≝
+   λR. R ∨ (R → False). 
+
 definition confluent: ∀A. ∀R1,R2: relation A. Prop ≝ λA,R1,R2.
                       ∀a0,a1. R1 a0 a1 → ∀a2. R2 a0 a2 →
                       ∃∃a. R2 a1 a & R1 a2 a.