Let x0 of type ι be given.
Let x1 of type ι → ι → ο be given.
Let x2 of type ι be given.
Let x3 of type ι → ο be given.
Assume H1:
∀ x4 . ∀ x5 : ι → ι → ο . ∀ x6 . prim1 x6 x4 ⟶ x3 (dd3c8.. x4 x5 x6).
Apply H1 with
x0,
x1,
x2.
The subproof is completed by applying H0.