calc
_ = iter f (m * n + m) a := rfl
_ = iter f (m * n) (iter f m a) := by rw [iter_add]
_ = iter (iter f m) n (iter f m a) := by rw [ih]
_ = iter (iter f m) (n + 1) a := by rw [iter_succ]
case succ
α : Sort u_1
f : α → α
m n : Nat
ih : ∀ (a : α), iter f (m * n) a = iter (iter f m) n a
a : α
⊢ iter f (m * (n + 1)) a = iter (iter f m) (n + 1) a
no goals