Let x0 of type ι be given.
Let x1 of type ι → ι be given.
Let x2 of type ι → ο be given.
Assume H1:
∀ x3 . ∀ x4 : ι → ι . (∀ x5 . prim1 x5 x3 ⟶ prim1 (x4 x5) x3) ⟶ x2 (c0301.. x3 x4).
Apply H1 with
x0,
x1.
The subproof is completed by applying H0.