Sergei A. Abramov A. A. Bogolubskaya V. A. Rostovtsev Victor F. Edneral The research seminar on computer algebra in 2004-2005. 61-64 2006 32 Programming and Computer Software 2 http://dx.doi.org/10.1134/S0361768806020010 db/journals/pcs/pcs32.html#AbramovBRE06