Let x0 of type ι be given.
Let x1 of type ι be given.
Let x2 of type ι → ι be given.
Let x3 of type ι → ι → ο be given.
Apply H0 with
λ x4 x5 . x1 = ap x5 0.
Let x4 of type ι → ι → ο be given.
The subproof is completed by applying tuple_3_0_eq with
x1,
lam x1 x2,
encode_r x1 x3,
λ x5 x6 . x4 x6 x5.