rw [extend_apply' _ _ _ (by simpa [embeddingOfSubset])]
α : Type u_1
β : Type u_2
γ : Type u_3
a : α
b : β
s : Set α
f✝ f : ↑s ↪ β
ha : a ∉ s
hb : b ∉ range ⇑f
⊢ extend (inclusion ⋯) (⇑f) (fun x => b) ⟨a, ⋯⟩ = b
no goals