Let x0 of type ι be given.
Let x1 of type ι be given.
Apply UPairE with
x1,
x0,
x0,
x1 = x0 leaving 3 subgoals.
The subproof is completed by applying H0.
Assume H1: x1 = x0.
The subproof is completed by applying H1.
Assume H1: x1 = x0.
The subproof is completed by applying H1.