Proofgold Proof

pf
Let x0 of type ι be given. Let x1 of type ι be given. Assume H0: x1 ∈ x0. Let x2 of type ι be given. Assume H1: x2 ∈ Sing x1. Apply SingE with x1, x2, λ x3 x4 . x4 ∈ x0 leaving 2 subgoals. The subproof is completed by applying H1. The subproof is completed by applying H0. ■