unfold Included in |- *.
auto.
Qed.
(*********************************************************************)
(*                  Some Results about ListSet                       *)
(*********************************************************************)
Section ListSetLemmas.
Variable A : Set.
Hypothesis Aeq_dec : forall x y : A, {x = y} + {x <> y}.

Lemma Set_union1 :
forall (B C : set A) (x : A),
set_In x (set_union Aeq_dec B C) -> ~ set_In x B -> set_In x C.