摘要：Submission Authors must use LaTeX for typewriting,and visit our website www.actamath.com to submit your paper.Our address is Editorial Office of Acta Mathematica Sinica,Academy of Mathematics and Systems Science,Chinese Academy of Sciences,Beijing 100190,PR R.China.All papers will be refereed.If necessary,the author(s)would be asked to revise the manuscript according to the referee's suggestions.