∀ {α : Type u_1} {β : Type u_2} [inst : TopologicalSpace α] [inst_1 : TopologicalSpace β] {f : α → β},
  Continuous f → ∀ {s u s' : Set β}, u ∈ nhdsSetWithin s s' → f ⁻¹' u ∈ nhdsSetWithin (f ⁻¹' s) (f ⁻¹' s')