(* Results about [pow_pos] and [pow_N] *)
Instance pow_ext : Proper (req ==> eq ==> req) (pow_pos rmul).
Instance pow_N_ext : Proper (req ==> eq ==> req) (pow_N rI rmul).

Lemma pow_pos_div a b p : ~ b == 0 ->
pow_pos rmul (a / b) p == pow_pos rmul a p / pow_pos rmul b p.