(** * Parity  - arities: (0, 1) *)
Definition parity_e : BC := (* 0 1 *)
comp 0 1 cond nil [proj 0 1 0; false_e 0 1; true_e 0 1; false_e 0 1].

Lemma parity_correct_even v :
bs2bool (sem parity_e nil [v]) = false ->
even (bs2nat v).