∀ {Γ : Type u_1} {R : Type u_3} {α : Type u_5} {β : Type u_6} [inst : AddCommMonoid Γ] [inst_1 : PartialOrder Γ]
  [inst_2 : IsOrderedCancelAddMonoid Γ] [inst_3 : Semiring R] (s : HahnSeries.SummableFamily Γ R α)
  (t : HahnSeries.SummableFamily Γ R β), s.hsum * t.hsum = (s.mul t).hsum