(** * Concatenation of bitstrings  - arities: (1, 1) *)
Definition app_e : BC :=
rec (proj 0 1 0)
(comp 1 2 (succ false) nil ((proj 1 2 1) :: nil))
(comp 1 2 (succ true) nil ((proj 1 2 1) :: nil)).

Lemma app_correct v1 v2 :
sem app_e [v1] [v2] = v1 ++ v2.