(** * Multiplication  - arities: (2,0) *)
Definition mult_e : BC :=
rec (zero_e 1 0)
(comp 2 1 plus_e ((proj 2 0 1) :: nil) ((proj 2 1 2) :: nil))
(comp 2 1 plus_e ((proj 2 0 1) :: nil) ((proj 2 1 2) :: nil)).

Lemma mult_correct :
forall m n, length (sem mult_e [m; n] nil) = (length m) * (length n).