proposition: Theorem two_power_pos_is_exp x y : two_power_pos (x + y) = two_power_pos x * two_power_pos y.
proof: Proof. rewrite 3 two_power_pos_equiv. now apply (Z.pow_add_r 2 (Zpos x) (Zpos y)). Qed.
imports: Wf_nat ZArith_base Zcomplements Zpow_def