Let x0 of type ι be given.
Let x1 of type ι be given.
Let x2 of type ι be given.
Assume H0:
In x2 (lam x0 (λ x3 . x1)).
Apply unknownprop_f8cb4609f9c174a593de5a10197e2915f5c1a2d9f32ed8d30c3d30b788bb9e1e with
λ x3 x4 : ι → ι → ι . In x2 (x4 x0 x1).
The subproof is completed by applying H0.