Let x0 of type ο be given.
Let x1 of type ο be given.
Let x2 of type ο be given.
Apply exactly1of3_E with
x0,
x1,
x2,
x2 ⟶ not x0 leaving 4 subgoals.
The subproof is completed by applying H0.
Assume H1: x0.
Assume H4: x2.
Apply H3 with
not x0.
The subproof is completed by applying H4.
Assume H2: x1.
Assume H4: x2.
Apply H3 with
not x0.
The subproof is completed by applying H4.
Assume H3: x2.
Assume H4: x2.
The subproof is completed by applying H1.