Let x0 of type ι be given.
Let x1 of type ι be given.
Let x2 of type ι be given.
Assume H0: x2 ∈ x0.
Assume H1: x2 ∈ x1.
Apply SepI with
x0,
λ x3 . x3 ∈ x1,
x2 leaving 2 subgoals.
The subproof is completed by applying H0.
The subproof is completed by applying H1.