Let x0 of type ι be given.
Let x1 of type ι → ι → ι be given.
Assume H0: ∀ x2 . x2 ∈ x0 ⟶ ∀ x3 . x3 ∈ x0 ⟶ x1 x2 x3 ∈ x0.
Let x2 of type ι → ο be given.
Let x3 of type ι → ο be given.
Assume H1:
∀ x4 . ∀ x5 : ι → ι → ι . (∀ x6 . x6 ∈ x4 ⟶ ∀ x7 . x7 ∈ x4 ⟶ x5 x6 x7 ∈ x4) ⟶ ∀ x6 : ι → ο . x3 (pack_b_p x4 x5 x6).
Apply H1 with
x0,
x1,
x2.
The subproof is completed by applying H0.