split <;> split at * <;> simp_all
case h
α : Sort u_1
β : Type u_2
f : α ⇀ β
a : α
⊢ (match
      match h : f a with
      | none => none
      | some b => some { val := b, property := ⋯ } with
    | some x => some ↑x
    | none => none) =
    f a
case h.h_1.h_2
α : Sort u_1
β : Type u_2
f : α ⇀ β
a : α
opt✝ : Option { b // ∃ a, f a = some b }
x✝ : { b // ∃ a, f a = some b }
b✝ : β
heq✝¹ : f a = some b✝
heq✝ : { val := b✝, property := ⋯ } = x✝
⊢ ↑x✝ = b✝