Opaque f'.
Definition smash'_e : BC :=
rec2 (proj 0 1 0) (comp 1 2 (succ false) nil [proj 1 2 1]).
(* Eval vm_compute in arities smash'_e. *)

Lemma smash'_correct x y :
sem smash'_e [x] [y] = smash' x y.