refine' ⟨fun h ↦ _, fun h ↦ by rw [h]⟩
α : Type u_1
ι : Type u_2
s t r : Set α
⊢ s \ (t ∩ s) = s \ (r ∩ s) ↔ t ∩ s = r ∩ s
α : Type u_1
ι : Type u_2
s t r : Set α
h : s \ (t ∩ s) = s \ (r ∩ s)
⊢ t ∩ s = r ∩ s