no goals
α : Type u_1
β : Type ?u.9322
inst✝¹ : TopologicalSpace α
inst✝ : TopologicalSpace β
s t s₁ s₂ t₁ t₂ : Set α
x : α
⊢ s ∈ 𝓝ˢ t ↔ ∃ U, IsOpen U ∧ t ⊆ U ∧ U ⊆ s
rw [← subset_interior_iff_mem_nhdsSet, subset_interior_iff]