1. Berestovskii V. N., “Homogeneous spaces with intrinsic metric,” Soviet Math. Dokl., vol. 38, no. 2, 60–63 (1989).
2. Pontryagin L. S., Boltyanskii V. G., Gamkrelidze R. V., and Mishchenko E. F., The Mathematical Theory of Optimal Processes, John Wiley and Sons, New York and London (1962).
3. Liu W. and Sussmann H. J., Shortest Parts for Sub-Riemannian Metrics on Rank–Two Distributions, Amer. Math. Soc., Providence (1996) (Mem. Amer. Math. Soc.; Vol. 564).
4. Mubarakzyanov G. M., “On solvable Lie algebras,” Izv. Vyssh. Uchebn. Zaved. Mat., vol. 1, 114–123 (1963).
5. Biggs R. and Remsing C., “On the classification of real four-dimensional Lie groups,” J. Lie Theory, vol. 26, no. 4, 1001–1035 (2016).