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