1．School of Sciences ,North China University of Technology ,Beijing 100041,China； 2．School of Math- ematics and Statistics ,Hebei University of Economy and Trade ,Shijiazhuang 050063,China；3．Department of Basic Courses ,Shijiazhuang Vocational Technology Institute ,Shijiazhuang 050081,China
About author:LIU Xi-bo（1962－）,male ,native of Kangbao ,Hebei ,an associate professor of North China University of Technology ,Ph．D．,engages in topology；YAO Li（1960－）,male ,native of Jinzhou ,Liaoning ,an associate professor of He- bei University of Economy and T rade ,engages in topology；WANG Yu-su（1961－）,female ,native of Fengrun ,Hebei ,an as- sociate professor of Shijiazhuang Vocational Technology Institute ,engages in topology .
