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

Lemma SUCC_intro2 :
forall (X : Typ1) (A : Rel X) (a : X),
ELT X A a (opt X) (SUCC X A a) (none X).