ι : Type ?u.343019
α : Type u
β : Type v
γ : Type w
δ : Type x
l₁ l₂ : List α
f : α → Option α
a b : α
l : List α
h : f a = some b
⊢ (match f a with
    | some b => b :: l
    | none => lookmap.go f l (Array.push #[] a)) =
    b :: l
ι : Type ?u.343019
α : Type u
β : Type v
γ : Type w
δ : Type x
l₁ l₂ : List α
f : α → Option α
a b : α
l : List α
h : f a = some b
⊢ lookmap f (a :: l) = b :: l
simp only [lookmap, lookmap.go, Array.toListAppend_eq, Array.data_toArray, nil_append]
no goals
ι : Type ?u.343019
α : Type u
β : Type v
γ : Type w
δ : Type x
l₁ l₂ : List α
f : α → Option α
a b : α
l : List α
h : f a = some b
⊢ (match f a with
    | some b => b :: l
    | none => lookmap.go f l (Array.push #[] a)) =
    b :: l
rw [h]