Proofgold Proof

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