Proofgold Proof

pf
Let x0 of type ι be given. Let x1 of type ι be given. Assume H0: x1 ⊆ V_ x0. Apply V_I with x1, x0, ordsucc x0 leaving 2 subgoals. The subproof is completed by applying ordsuccI2 with x0. The subproof is completed by applying H0. ■