Let x0 of type ο be given.
Let x1 of type ο be given.
Assume H1: x1.
Apply orIR with
and x0 (not x1),
and (not x0) x1.
Apply andI with
not x0,
x1 leaving 2 subgoals.
The subproof is completed by applying H0.
The subproof is completed by applying H1.