Unique Normal Forms for Nilpotent Planar Vector Fields.

Guoting Chen Duo Wang Xiaofeng Wang Unique Normal Forms for Nilpotent Planar Vector Fields. 2159-2174 2002 12 I. J. Bifurcation and Chaos 10 http://dx.doi.org/10.1142/S0218127402005741 db/journals/ijbc/ijbc12.html#ChenWW02