Let x0 of type ι be given.
Let x1 of type ι → ο be given.
Assume H0:
∀ x2 . x1 x2 ⟶ ∀ x3 . x3 ∈ x2 ⟶ nIn x0 x3.
Let x2 of type ι be given.
Apply Eps_i_ex with
λ x3 . and (x1 x3) (∃ x4 . and (x1 x4) (x2 = pair_tag x0 x3 x4)).
The subproof is completed by applying H1.