proposition: Lemma binds_weaken : binds x a (E ++ G) -> binds x a (E ++ F ++ G).
proof: Proof. clear. intros. solve_binds. Qed.
imports: Coq.FSets.FSets Coq.Lists.List Coq.Logic.Decidable Metalib.CoqFSetDecide Metalib.CoqListFacts Metalib.LibTactics Metalib.MetatheoryAtom Metalib.LibTactics