| Description: Virtual deduction proof of nfra2 3376.  The following user's proof is
       completed by invoking mmj2's unify command and using mmj2's
       StepSelector to pick all remaining steps of the Metamath proof. 
       (Contributed by Alan Sare, 31-Dec-2011.)  (Proof modification is
       discouraged.)  (New usage is discouraged.) | 1:: | ⊢ (∀𝑦 ∈ 𝐵∀𝑥 ∈ 𝐴𝜑 →
       ∀𝑦∀𝑦 ∈ 𝐵∀𝑥 ∈ 𝐴𝜑) |   | 2:: | ⊢ (∀𝑥 ∈ 𝐴∀𝑦 ∈ 𝐵𝜑 ↔
       ∀𝑦 ∈ 𝐵∀𝑥 ∈ 𝐴𝜑) |   | 3:1,2,?: e00 44788 | ⊢ (∀𝑥 ∈ 𝐴∀𝑦 ∈ 𝐵𝜑 →
       ∀𝑦∀𝑦 ∈ 𝐵∀𝑥 ∈ 𝐴𝜑) |   | 4:2: | ⊢ ∀𝑦(∀𝑥 ∈ 𝐴∀𝑦 ∈ 𝐵𝜑 ↔
       ∀𝑦 ∈ 𝐵∀𝑥 ∈ 𝐴𝜑) |   | 5:4,?: e0a 44792 | ⊢ (∀𝑦∀𝑥 ∈ 𝐴∀𝑦 ∈ 𝐵𝜑 ↔
       ∀𝑦∀𝑦 ∈ 𝐵∀𝑥 ∈ 𝐴𝜑) |   | qed:3,5,?: e00 44788 | ⊢ (∀𝑥 ∈ 𝐴∀𝑦 ∈ 𝐵𝜑 →
       ∀𝑦∀𝑥 ∈ 𝐴∀𝑦 ∈ 𝐵𝜑) |  |