rw [← image_singleton, ← openEmbedding_coe.open_iff_image_open]
case intro
α : Type u_1
β : Type u_2
ι : Type u_3
s : Set α
n : ℕ∞
x : ℕ
⊢ IsOpen {↑x}
case intro
α : Type u_1
β : Type u_2
ι : Type u_3
s : Set α
n : ℕ∞
x : ℕ
⊢ IsOpen {x}