(** we now generalize the theorem to the nth-root *)
Fixpoint power (x n:nat) {struct n} : nat :=
  match n with
    O => 1
    | (S n) => (x*(power x n))
  end.

Lemma power_plus_lemma1 : forall (n m x:nat),(power x (n+m))=(power x n)*(power x m).