exact λ U hU => mem_of_superset hU (λ ⟨x, y⟩ hxy hx => mem_biUnion hx hxy)
ι : Type u_1
α : Type u_2
β : Type u_3
a : α
s t : Set α
x u v : Set (α × α)
p : Filter ι
inst✝ : UniformSpace α
⊢ ∀ s_1 ∈ 𝓤 α, ∀ᶠ (x : α × α) in 𝓤 α, x ∈ Prod.fst ⁻¹' s → x.2 ∈ thickening s_1 s
no goals