+definition singlevalued: ∀A,B. predicate (relation2 A B) ≝ λA,B,R.
+ ∀a,b1. R a b1 → ∀b2. R a b2 → b1 = b2.
+
+(* Reflexive closure ************)
+
+definition RC: ∀A:Type[0]. relation A → relation A ≝
+ λA,R,x,y. R … x y ∨ x = y.
+
+lemma RC_reflexive: ∀A,R. reflexive A (RC … R).
+/2 width=1/ qed.
+