Let x0 of type ι be given.
Let x1 of type ι → ι → ι be given.
Let x2 of type ι be given.
Assume H0: x2 ∈ x0.
Let x3 of type ι be given.
Assume H1: x3 ∈ x0.
Assume H2: ∀ x4 . x4 ∈ x0 ⟶ x1 x2 x4 = x4.
Assume H3: ∀ x4 . x4 ∈ x0 ⟶ x1 x4 x3 = x4.
Apply H3 with
x2,
λ x4 x5 . x4 = x3 leaving 2 subgoals.
The subproof is completed by applying H0.
Apply H2 with
x3.
The subproof is completed by applying H1.