1. Karmanova M. B., “The polynomial sub-Riemannian differentiability of some Hölder mappings of Carnot groups,” Sib. Math. J., vol. 58, No. 2, 232–254 (2017).
2. Basalaev S. G. and Vodopyanov S. K., “Approximate differentiability of mappings of Carnot–Carathéodory spaces,” Eurasian Math. J., vol. 4, No. 2, 10–48 (2013).
3. Gromov M., “Carnot–Carathéodory spaces seen from within,” in: Sub-Riemannian Geometry, Birkhäuser-Verlag, Basel, 1996, 79–318.
4. Karmanova M. and Vodopyanov S., “Geometry of Carnot–Carathéodory spaces, differentiability, coarea and area formulas,” in: Analysis and Mathematical Physics, Birkhäuser, Basel, 2009, 233–335.
5. Nagel A., Stein E. M., and Wainger S., “Balls and metrics defined by vector fields. I. Basic properties,” Acta Math., vol. 155, 103–147 (1985).