Proof
fun X A a x' H E _ H2 _ =>
H2 x' (eq_refl (opt X) (none X)) (eq_refl (opt X) (some X x')) H.

Lemma SUCC_rt2 :
forall (X : Typ1) (A : Rel X) (a : X), SUCC X A a (some X a) (none X).