∀ {Γ : Type u_1} {R : Type u_3} [inst : AddCommMonoid Γ] [inst_1 : LinearOrder Γ] [inst_2 : IsOrderedCancelAddMonoid Γ]
  [inst_3 : NonUnitalNonAssocSemiring R] {x y : HahnSeries Γ R},
  x.leadingCoeff * y.leadingCoeff ≠ 0 → (x * y).orderTop = x.orderTop + y.orderTop