Let x0 of type ι → ι → ο be given.
Apply unknownprop_561892459e3cf9bb2fd1479e798d3d83f76d3fa1e0328e2070f23e32c38d47b3 with
λ x1 x2 : (ι → ι → ο) → ο . (∀ x3 x4 . x0 x3 x4 ⟶ x0 x4 x3 ⟶ x3 = x4) ⟶ x2 x0.
Assume H0: ∀ x1 x2 . x0 x1 x2 ⟶ x0 x2 x1 ⟶ x1 = x2.
The subproof is completed by applying H0.