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