Proofgold Proof

The subproof is completed by applying andI with ∀ x3 . x3 ∈ x0 ⟶ x2 x3 ∈ x1, ∀ x3 . x3 ∈ x0 ⟶ ∀ x4 . x4 ∈ x0 ⟶ x2 x3 = x2 x4 ⟶ x3 = x4.