simp
m : Type u → Type u_1
inst✝¹ : Monad m
inst✝ : LawfulMonad m
n : ℕ
β : Type u
init : β
f : Fin n → β → m β
this :
  ∀ (i j : ℕ) (hj : i + j = n) (macc : m β),
    (do
        let acc ← macc
        foldlM.aux n f i acc) =
      foldl.loop n (?m.30970 i j hj macc) macc i
⊢ 0 + n = n
no goals