proposition: Lemma fresh_app_l : uniq (F ++ E) -> binds x a E -> x `notin` dom F.
proof: Proof. clear. intros. assert (x `in` dom E) by eauto using binds_In. solve_uniq. Qed.
imports: Coq.FSets.FSets Coq.Lists.List Coq.Logic.Decidable Metalib.CoqFSetDecide Metalib.CoqListFacts Metalib.LibTactics Metalib.MetatheoryAtom Metalib.LibTactics