Let x0 of type ι be given.
Let x1 of type ι be given.
Let x2 of type ι be given.
Let x3 of type ι be given.
Let x4 of type ι be given.
Apply beta with
5,
λ x5 . If_i (x5 = 0) x0 (If_i (x5 = 1) x1 (If_i (x5 = 2) x2 (If_i (x5 = 3) x3 x4))),
1,
λ x5 x6 . x6 = x1 leaving 2 subgoals.
The subproof is completed by applying In_1_5.
Apply If_i_0 with
1 = 0,
x0,
If_i (1 = 1) x1 (If_i (1 = 2) x2 (If_i (1 = 3) x3 x4)),
λ x5 x6 . x6 = x1 leaving 2 subgoals.
The subproof is completed by applying neq_1_0.
Apply If_i_1 with
1 = 1,
x1,
If_i (1 = 2) x2 (If_i (1 = 3) x3 x4).
Let x5 of type ι → ι → ο be given.
Assume H0: x5 1 1.
The subproof is completed by applying H0.