proposition: Lemma fresh_mid_head : uniq (F ++ (x ~ a) ++ E) -> ~ In x (dom F).
proof: Proof. clear. solve_uniq. Qed.
imports: Coq.FSets.FSets Coq.Lists.List Coq.Logic.Decidable Coq.Strings.String String Metalib.CoqFSetDecide Metalib.CoqListFacts Metalib.LibTactics Metalib.CoqFSetInterface Coq.Classes.Equivalence Coq.Classes.EquivDec Metalib.CoqEqDec