intros x y z x0 y0; unfold Rpower.
rewrite <- exp_plus, ln_mult, Rmult_plus_distr_l; auto.
Qed.

(* Specifications: *)
Lemma Rlt_Rpower_l a b c: 0 < c -> 0 < a < b -> Rpower a c < Rpower b c.
Lemma Rle_Rpower_l a b c: 0 <= c -> 0 < a <= b -> Rpower a c <= Rpower b c.
Definition arcsinh x := ln (x + sqrt (x ^ 2 + 1)).