Let x0 of type ο be given.
Let x1 of type ο be given.
Let x2 of type ο be given.
Assume H2: x2.
Apply orIR with
and (exactly1of2 x0 x1) (not x2),
and (and (not x0) (not x1)) x2.
Apply and3I with
not x0,
not x1,
x2 leaving 3 subgoals.
The subproof is completed by applying H0.
The subproof is completed by applying H1.
The subproof is completed by applying H2.