Let x0 of type ο be given.
Let x1 of type ο be given.
Apply exactly1of2_E with
x0,
x1,
x1 ⟶ not x0 leaving 3 subgoals.
The subproof is completed by applying H0.
Assume H1: x0.
Assume H3: x1.
Apply H2 with
not x0.
The subproof is completed by applying H3.
Assume H2: x1.
Assume H3: x1.
The subproof is completed by applying H1.