proposition: Lemma env_subset_sum_r : forall E El Er, envSubset E Er -> envSubset E (El [+] Er).
proof: Proof. intros; intros x A D. apply env_sum_ry. apply H; trivial. Qed.
imports: CoLoR(RelExtras ListExtras TermsLifting LogicUtil OptUtil) Coq(Arith Setoid Morphisms Lia)