Definition Succ_e : Cobham :=
Comp 1 (Succ true) [Proj 1 0].
Opaque Succ_e.
Fixpoint Nat_e (n:nat) : Cobham :=
match n with
| 0 => Zero
| S n' => Comp 0 Succ_e [Nat_e n']
end.

Lemma arity_Nat n : arity (Nat_e n) = ok_arity 0.