Proof strictsub_trans1_Out.
(***** we should also do StrictSUB_trans2 using assumption StrictSUB B C ***)
(*** ??? ***)
(***********************************)
(********* the empty set ***********)
(***********************************)
Section emptyset_empty.
Variable X : Ens.
Hypothesis h : IN X EmptySet.

Lemma emptyset_empty_Out : False.
Proof EmptySet_pr X h.