Opaque Poly_pow.
Definition Poly_mon (ar:nat)(m:mon) : Cobham :=
Comp ar Mult_e [Comp ar (Nat_e (fst m)) nil; Multl_e ar (map (Poly_pow ar) (snd m))].

Lemma arity_Poly_mon : forall ar m,
pWF_mon ar m ->
arity (Poly_mon ar m) = ok_arity ar.