(** Injectivity *)

(* Specifications: *)
Lemma pow_inj_l : forall a b c, 0<=a -> 0<=b -> 0<c ->
a^c == b^c -> a == b.
Lemma pow_inj_r : forall a b c, 1<a -> 0<=b -> 0<=c ->
a^b == a^c -> b == c.