Chebotar, M. A.M. A.ChebotarKe, W. F.W. F.KeLee, P. H.P. H.Lee2010-10-152018-06-282010-10-152018-06-282004-10http://ntur.lib.ntu.edu.tw//handle/246246/215965en-USMaps characterized by action on zero productsjournal article