Let x0 of type ο be given.
Let x1 of type ο be given.
Let x2 of type ο be given.
Let x3 of type ο be given.
Assume H0:
or (or (or x0 x1) x2) x3.
Let x4 of type ο be given.
Assume H1: x0 ⟶ x4.
Assume H2: x1 ⟶ x4.
Assume H3: x2 ⟶ x4.
Assume H4: x3 ⟶ x4.
Apply H0 with
x4 leaving 2 subgoals.
Assume H5:
or (or x0 x1) x2.
Apply or3E with
x0,
x1,
x2,
x4 leaving 4 subgoals.
The subproof is completed by applying H5.
The subproof is completed by applying H1.
The subproof is completed by applying H2.
The subproof is completed by applying H3.
The subproof is completed by applying H4.