proposition: Lemma le_sigma_xi_yi : (sigma_xi c0 >= sigma_yi c0)%Z.
proof: Proof. unfold sigma_xi, sigma_yi in |- *; apply ge_sigma_sigma. intros; apply le_xi_yi. Qed.
imports: copy del rece_copy1 rece_copy2 rece_copy3 rece_dec rece_inc