1. Baikov VA, Gazizov RK, Ibragimov NH (1989) Math. USSR-Sbornik. 64:427
2. Baikov VA, Gazizov RK, Ibragimov NH (1991) J Sov Math 55:1450
3. Kovalev VF, Pustovalov VV Shirkov DV (1998) Math Phys 39:1170 hep-th/9706056
4. Kovalev VF, Shirkov DV (2008) Renormalization-group symmetries for solutions of nonlinear boundary value problems, Physics-Uspekhi 51(8):815–830; Prepint arXiv:math-ph/0812.4821
5. Ibragimov NH, Kovalev VF (2009) Approximate and Renormgroup symmetries. In: Luo AC, Ibragimov NH (eds) Nonlinear physical science. Higher Education Press & Springer, ISBN 978-3-642-0027-4, ISBN 978-7-04-026159-3 (2009)