proposition: Lemma disjoint_cons_1 : forall A B x a (E : list (X.t*A)) (F : list (X.t*B)), disjoint ((x, a) :: E) F -> ~ In x (dom F).
proof: Proof. unfold disjoint. simpl. fsetdec. 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