Proofgold Proof

pf
Let x0 of type ι be given. Let x1 of type ι be given. Let x2 of type ι be given. Assume H0: x2 ∈ x1. Assume H1: x2 ∈ setminus x0 x1. Apply setminusE2 with x0, x1, x2 leaving 2 subgoals. The subproof is completed by applying H1. The subproof is completed by applying H0. ■