proposition: Lemma eq_pair_dec : forall x y : A*B, {x=y}+{~x=y}.
proof: Proof. intros (x1,x2) (y1,y2). case (eqdecA x1 y1); intro. subst y1. case (eqdecB x2 y2); intro. subst y2. auto. right. unfold not. intro. injection H. intro. cong. right. unfold not. intro. injection H. intros. cong. Qed.
imports: CoLoR(LogicUtil)