@article{ZNSL_1986_155_a1,
     author = {A. M. Vershik and V. Ya. Gershkovich},
     title = {Geodesic flow on $SL_2\mathbb R$ with non-holonomic constraints},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {7--17},
     publisher = {mathdoc},
     volume = {155},
     year = {1986},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1986_155_a1/}
}