Abdul Salam Jarrah Reinhard C. Laubenbacher Valery Romanovski The Sibirsky component of the center variety of polynomial differential systems. 577-589 2003 35 J. Symb. Comput. 5 http://dx.doi.org/10.1016/S0747-7171(03)00016-6 db/journals/jsc/jsc35.html#JarrahLR03