Hint Rewrite @subst_lift1 (*@subst_lift1'*) @subst_lift1C  : subst.

Lemma subst_lift2:
forall {A1 A2 B} id v (f: A1 -> A2 -> B) a b,
subst id v (lift2 f a b) = lift2 f (subst id v a) (subst id v b).