have ⟨L,hL⟩ := xs.exists_rep
α : Type u_1
f : α → Bool
h : ∀ (a1 a2 : α), f a1 = true → f a2 = true → a1 = a2
x : α
xs : Multiset α
⊢ find? f xs h = some x ↔ x ∈ xs ∧ f x = true
α : Type u_1
f : α → Bool
h : ∀ (a1 a2 : α), f a1 = true → f a2 = true → a1 = a2
x : α
xs : Multiset α
L : List α
hL : ⟦L⟧ = xs
⊢ find? f xs h = some x ↔ x ∈ xs ∧ f x = true