Let x0 of type ι be given.
Apply orIR with
x0 ∈ x0,
and (x0 = x0) (u1 ∈ u4).
Apply andI with
x0 = x0,
u1 ∈ u4 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_1_4.