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