Fixpoint unary_preserv (e : BC) : bool :=
match e with
| zero => true
| proj n s j => true
| succ b => b
| pred => true
| cond => true
| rec g h0 h1 => unary_preserv g  &&
unary_preserv h0 &&
unary_preserv h1
| comp _ _ h nl sl => unary_preserv h &&
forallb unary_preserv nl &&
forallb unary_preserv sl
end.
(** * Zero  - with any arities (n, s) *)

Lemma zero_correct n s l1 l2:
length (sem (zero_e n s) l1 l2) = 0.