Universal Unfolding of SaddleSingularity of Codimension 3 of aPlanar Vector Field With NilpotentLinear Part,Xiao Dongmei(肖冬梅),Peking University,Supervisor:ZhangZhifen(张芷芬),Approved:1991,7. In this paper the universal unfo-Iding is studied for a singular vectorfield whose 3-jet is c~∞ equivalent to