no goals
α : Type u_1
β : Type u_2
γ : Type ?u.196791
δ : Type ?u.196794
inst✝² : TopologicalSpace α
inst✝¹ : TopologicalSpace β
inst✝ : TopologicalSpace γ
f : α → β
hf : IsOpenMap f
hfc : Continuous f
s : Set β
⊢ f ⁻¹' frontier s = frontier (f ⁻¹' s)
simp only [frontier_eq_closure_inter_closure, preimage_inter, preimage_compl,
  hf.preimage_closure_eq_closure_preimage hfc]