Lemma Zquot_mul: forall m l, l >= 0 -> two_p (N+l) < m * d <= two_p (N+l) + two_p l -> forall n, - two_p N <= n < two_p N -> Z.quot n d = Z.div (m * n) (two_p (N + l)) + (if zlt n 0 then 1 else 0).