End A_sub_V_proof.
Let A_sub_V : SUB A V. Proof A_sub_V_proof_Out.
Section B_sub_V_proof.
Variable Z : Ens.
Hypothesis h2 : IN Z B.
Section B_sub_V_proof1.
Hypothesis h3 : EQ X Z.
Let step1_1 : IN X B.
Proof Extensionality X Z B h3 h2.

Lemma B_sub_V_proof1_Out : False.
Proof k step1_1.