∀ {X : Type u_5} [inst : TopologicalSpace X] {k : WithTop ℕ∞} {E : Type u_1} {H : Type u_2}
  [inst_1 : NormedAddCommGroup E] [inst_2 : NormedSpace ℝ E] [inst_3 : FiniteDimensional ℝ E]
  [inst_4 : TopologicalSpace H] {I : ModelWithCorners ℝ E H} (s : SingularManifold X k I) (t : SingularManifold X k I),
  BoundarylessManifold I (s.M ⊕ t.M)