Let x0 of type ι be given.
Let x1 of type ι be given.
Apply V_E with
x0,
x1,
V_ x0 ∈ V_ x1 leaving 2 subgoals.
The subproof is completed by applying H0.
Let x2 of type ι be given.
Assume H1: x2 ∈ x1.
Apply V_I with
V_ x0,
x2,
x1 leaving 2 subgoals.
The subproof is completed by applying H1.
Apply V_Subq_2 with
x0,
x2.
The subproof is completed by applying H2.