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,
or (or x0 x1) x2 leaving 4 subgoals.
The subproof is completed by applying H0.
Assume H1: x0.
Apply or3I1 with
x0,
x1,
x2.
The subproof is completed by applying H1.
Assume H2: x1.
Apply or3I2 with
x0,
x1,
x2.
The subproof is completed by applying H2.
Assume H3: x2.
Apply or3I3 with
x0,
x1,
x2.
The subproof is completed by applying H3.