fact: Axiom binds_app_iff : binds x a (E ++ F) <-> binds x a E \/ binds x a F.
imports: Coq.FSets.FSets Coq.Lists.List Coq.Logic.Decidable Metalib.CoqFSetDecide Metalib.CoqListFacts Metalib.AssocList Metalib.MetatheoryAtom Metalib.LibTactics