Let x0 of type ι → ο be given.
Let x1 of type ι → ο be given.
Assume H0: ∀ x2 . x0 x2 ⟶ x1 x2.
Assume H1: ∀ x2 . x1 x2 ⟶ x0 x2.
Apply functional extensionality with
x0,
x1.
Let x2 of type ι be given.
Apply prop_ext_2 with
x0 x2,
x1 x2 leaving 2 subgoals.
The subproof is completed by applying H0 with x2.
The subproof is completed by applying H1 with x2.