Let x0 of type ι be given.
Apply orIR with
x0 ∈ x0,
and (x0 = x0) (0 ∈ u3).
Apply andI with
x0 = x0,
0 ∈ u3 leaving 2 subgoals.
Let x1 of type ι → ι → ο be given.
Assume H1: x1 x0 x0.
The subproof is completed by applying H1.
The subproof is completed by applying In_0_3.