\Bibitem{1} \paper To the 70th birthday of Professor Mukhtarbai Otelbaev \jour Eurasian Math. J. \yr 2012 \vol 3 \issue 2 \pages 5--11 \mathnet{http://mi.mathnet.ru/emj82} \mathscinet{http://mathscinet.ams.org/mathscinet-getitem?mr=3024116}