Proofgold Proof

pf
Let x0 of type ι be given. Let x1 of type ι be given. Let x2 of type ι be given. Let x3 of type ι be given. Assume H0: setsum x2 x3 ∈ setprod x0 x1. Apply pair_Sigma_E1 with x0, λ x4 . x1, x2, x3. The subproof is completed by applying H0. ■