Proofgold Proof

pf
Let x0 of type ι be given. Let x1 of type ι be given. Assume H0: nIn x0 x1. Assume H1: x1 = Sing x0. Apply H0. Apply H1 with λ x2 x3 . x0 ∈ x3. The subproof is completed by applying SingI with x0. ■