Shuming Gao Huagen Wan Qunsheng Peng Constraint-Based Virtual Solid Modeling. 56-63 2000 15 J. Comput. Sci. Technol. 1 http://jcst.ict.ac.cn/cone/cone01.html#paper6 db/journals/jcst/jcst15.html#GaoWP00