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: x0 ⊆ x1. Assume H1: nIn x2 x1. Assume H2: x2 ∈ x0. Apply H1. Apply H0 with x2. The subproof is completed by applying H2. ■