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