环面的生成元不必是圆，而可以是椭圆或任何圆锥曲线,一个环面是两个圆的乘积

http://zh.wikipedia.org/wiki/%E7%8E%AF%E9%9D%A2

http://home.ustc.edu.cn/~aiwanjun/lecture_notes/

Index of /~aiwanjun/lecture_notes

 Name                                 Last modified      Size  Description

 Parent Directory                                          -   
 Algebra_Topology_wangxiangjun.pdf    30-Aug-2012 00:40  377K  
 Conformal_Trans.pdf                  05-Dec-2012 10:44  193K  
 Han_Qin.pdf                          30-Aug-2012 00:41  101K  
 Riemannian_Lorenz_Geometry.pdf       30-Aug-2012 00:41  104K  
 SympleticMani.pdf                    30-Aug-2012 00:41  396K  
 curvatute_80s.pdf                    30-Aug-2012 00:41  4.1M  
 notes_on_riemann_fensler_geomety.pdf 30-Aug-2012 00:41  716K  
 wulff_flow.pdf                       30-Aug-2012 00:42  258K  

Apache/2.0.52 (Red Hat) Server at home.ustc.edu.cn Port 80