We discuss this problem. Using the method in and an estimated due to Norton and Bates , we get Theorem 1 an d Theorem 2. They partially generalize the main theorem in .

• 本文讨论了这个问题 ；应用 [8]中方法和 Norton[5]和 Bates[1 ]的估计 ；我们得到了定理 1和定理 2 .；它们部分地推广了 [8]中主要定理