intuition.
rewrite <- (group_cyclic g x).
rewrite <- (group_cyclic g y).
repeat rewrite <- groupExp_plus.
f_equal.
omega.
apply g_generator.
apply g_generator.
Qed.

(* Specifications: *)
Theorem groupExp_distrib : forall n x y,
(x * y)^n = x^n * y^n.