simp [find?]
case cons
α : Type u_1
a b : List α
f : α → Bool
hunique : ∀ (a1 a2 : α), f a1 = true → f a2 = true → a1 = a2
x✝ : α
l₁✝ l₂✝ : List α
a✝ : l₁✝ ~ l₂✝
a_ih✝ : find? f l₁✝ = find? f l₂✝
⊢ find? f (x✝ :: l₁✝) = find? f (x✝ :: l₂✝)
case cons
α : Type u_1
a b : List α
f : α → Bool
hunique : ∀ (a1 a2 : α), f a1 = true → f a2 = true → a1 = a2
x✝ : α
l₁✝ l₂✝ : List α
a✝ : l₁✝ ~ l₂✝
a_ih✝ : find? f l₁✝ = find? f l₂✝
⊢ (match f x✝ with
    | true => some x✝
    | false => find? f l₁✝) =
    match f x✝ with
    | true => some x✝
    | false => find? f l₂✝