Let x0 of type ι → ι → ο be given.
Let x1 of type ι be given.
Let x2 of type ι be given.
Apply pack_e_0_eq2 with
x1,
x2,
λ x3 x4 . x0 x3 (ap (pack_e x1 x2) 1) = x0 x1 x2.
Apply pack_e_1_eq2 with
x1,
x2,
λ x3 x4 . x0 x1 x3 = x0 x1 x2.
Let x3 of type ο → ο → ο be given.
Assume H0: x3 (x0 x1 x2) (x0 x1 x2).
The subproof is completed by applying H0.