have := hb ▸ h b
α : Type u_1
β b✝¹ : Type u_2
f : α ⇀ β
b✝ : b✝¹
a : α
b : β
hb : f a = some b
h : ∀ (b : β), f a ≠ some b
⊢ False
α : Type u_1
β b✝¹ : Type u_2
f : α ⇀ β
b✝ : b✝¹
a : α
b : β
hb : f a = some b
h : ∀ (b : β), f a ≠ some b
this : some b ≠ some b
⊢ False