Proof
fun X A a E _ _ H3 =>
H3 (eq_refl (opt X) (none X)) (eq_refl (opt X) (some X a)).

Lemma SUCC_eqv :
forall (X : Typ1) (A : Rel X) (a x : X),
EQV X A x (opt X) (SUCC X A a) (some X x).