Let x0 of type ι → ι → ο be given.
Let x1 of type ι be given.
Let x2 of type ι be given.
Let x3 of type ι be given.
Assume H1: x0 x1 x2.
Assume H2: x0 x3 x2.
Apply H0 with
x0 x1 x3.
Apply H4 with
x1,
x2,
x3 leaving 2 subgoals.
The subproof is completed by applying H1.
Apply H3 with
x3,
x2.
The subproof is completed by applying H2.