fact: Axiom fresh_app_l : uniq (F ++ E) -> binds x a E -> ~ In x (dom F).
imports: Coq.FSets.FSets Coq.Lists.List Coq.Logic.Decidable Metalib.CoqFSetDecide Metalib.CoqListFacts Metalib.AssocList Metalib.MetatheoryAtom Metalib.LibTactics