� 1 − e � �� −τ hx ≪ hx −τ−1 , ∂ ∂x and taking into c<strong>on</strong>siderati<strong>on</strong> that <strong>the</strong> O-c<strong>on</strong>stant in (1) depends <strong>on</strong>ly <strong>on</strong> <strong>the</strong> O-c<strong>on</strong>stant in (3). Lemma 2: We have (2) if for a suitable η > 0. sup N
We sh<str<strong>on</strong>g>all</str<strong>on</strong>g> prove <strong>the</strong> following lemma by adapting a method of Heath-Brown (see [11, page 257]). Lemma 4: Let Qh be any positive integer. Then |Lh| 2 � ≪ QhX � hX λ Y λ Q −1 �1/2 � h Q −1 h Y 2 + Y � Then Proof: For q ∈ � we define <strong>the</strong> interval Iq by Iq := � Y λ (q − 1)/Qh, Y λ � q/Qh . |Lh| ≪ � q≤2Qh � m∼X | � n ∼ Y, n λ ∈ Iq, mn ∼ N � 2−λ + QhX h −1 Y 2−λ + Y X λ�� (log N). bne � hm λ n λ� |. From that, using <strong>the</strong> Cauchy-Schwarz inequality, we obtain |Lh| 2 ≪ QhX � � | � bne � hm λ n λ� | 2 q≤2Qh ≪ QhX � q≤2Qh ≪ QhX � m∼X � n ∼ Y, n λ ∈ Iq n, r ∼ Y, |t| ≤ 2Y λ /Qh n ∼ Y, nλ ∈ Iq, mn ∼ N � r ∼ Y, r λ ∈ Iq | � m ∼ X, mn ∼ N, mr ∼ N | � m ∼ X, mn ∼ N, mr ∼ N e � h(n λ − r λ )m λ� | e � htm λ� |, (5) where we put t := n λ − r λ . Applying [11, Lemma 1] to <strong>the</strong> inner sum in <strong>the</strong> last line of (5), we get � m ∼ X, mn ∼ N, mr ∼ N e � htm λ� � ≪ min X, (ht) −1 X 1−λ + � htX λ�1/2 � ≤ � htX λ� 1/2 + X min � 1, (ht) −1 X −λ� . (6) Combining (5) and (6), and using partial summati<strong>on</strong>, we obtain where |Lh| 2 ≪ QhX � hX λ Y λ Q −1 �1/2 h S � 2Y λ Q −1 � h + QhX 2 S � h −1 X −λ� + h −1 QhX 2−λ (log N) max ∆≥h−1X −λ S(∆)∆−1 , (7) 5