∀ {R : Type u_1} [inst : TopologicalSpace R] [inst_1 : Semiring R] [inst_2 : IsSemitopologicalSemiring R]
  (s : Subsemiring R) {a b : R},
  a ∈ s.toAddSubmonoid.topologicalClosure.carrier →
    b ∈ s.toAddSubmonoid.topologicalClosure.carrier → a + b ∈ s.toAddSubmonoid.topologicalClosure.carrier