Let x0 of type ι → ι → ο be given.
Let x1 of type ι be given.
Let x2 of type ι be given.
Assume H0: x0 x1 x2.
Let x3 of type ι → ι → ο be given.
Assume H1: ∀ x4 x5 . x0 x4 x5 ⟶ x3 x4 x5.
Assume H2: ∀ x4 x5 x6 . x3 x4 x5 ⟶ x3 x5 x6 ⟶ x3 x4 x6.
Apply H1 with
x1,
x2.
The subproof is completed by applying H0.