proposition: Lemma case_eq : forall (E F : Set) (eq_E_dec : eq_dec E) (x : E) (y z : F), match eq_E_dec x x with | left _ => y | right _ => z end = y.
proof: Proof. intros; case (eq_E_dec x x). auto. intros; absurd (x = x); auto. Qed.
imports: Arith Omega List