no goals
α : Type u
β : Type v
ι : Sort w
a : α
s✝ s₁ s₂ t : Set α
p p₁ p₂ : α → Prop
inst✝ : TopologicalSpace α
s : Set α
x : α
⊢ x ∈ interior s ↔ ∃ t, t ⊆ s ∧ IsOpen t ∧ x ∈ t
simp only [interior, mem_sUnion, mem_setOf_eq, and_assoc, and_left_comm]