proposition: Lemma Empty_R_neutral_union_l : forall R x y, union _ R Empty_R x y <-> R x y.
proof: Proof. intros R x y. rewrite union_sym. apply Empty_R_neutral_union_r. Qed.
imports: Coq(Relations List Setoid) CoLoR(weaved_relation closure equational_theory_spec dp modular_dp terminaison)