ALEKSEEVSKIY, Dmitry, Alexandr MEDVEDEV and
Jan SLOVÁK. Constant curvature models in sub-Riemannian geometry.
Journal of Geometry and Physics. Amsterdam: Elsevier Science BV, 2019, vol. 138, April, p. 241-256. ISSN 0393-0440. Available from: https://dx.doi.org/10.1016/j.geomphys.2018.09.013.