∀ {ι : Type u_1} {α : Type u_3} {L : SummationFilter ι} [inst : DivisionSemiring α] [inst_1 : TopologicalSpace α]
  [IsTopologicalSemiring α] {f : ι → α} {a : α} [T2Space α], a * ∑'[L] (x : ι), f x = ∑'[L] (x : ι), a * f x