Definition concat := smash'_e.Definition poly_BC_pow (ar:nat)(xn:pow) : BC :=
  multl_e ar (repeat (snd xn) (proj ar 0 (fst xn))).

Lemma poly_BC_pow_arities : forall ar xn, pWF_pow ar xn -> arities (poly_BC_pow ar xn) = ok_arities ar 0.