∀ {α : Type u_3} {A : Type u_4} [inst : AddCommMonoid A] [inst_1 : Finset.HasAntidiagonal A]
  [inst_2 : TopologicalSpace α] [inst_3 : NonUnitalNonAssocSemiring α] {f g : A → α},
  (Summable fun x => f x.1 * g x.2) ↔ Summable fun x => f (↑x.snd).1 * g (↑x.snd).2