Surfaces in three-dimensional Lie groups. Berdinskij, D.A.; Tajmanov, I.A. — 2005 Sibirskij Matematicheskij Zhurnal
Surfaces of revolution in the Heisenberg group and the spectral generalization of the Willmore functional. Berdinskij, D.A.; Tajmanov, I.A. — 2007 Sibirskij Matematicheskij Zhurnal