1. S. G. Basalaev, “One-Dimensional Level Sets of $$hc
$$-Differentiable Mappings
of Carnot–Carathéodory Spaces,” Vestn. Novosib. Gos. Univ., Ser. Mat. Mekh. Inform.
4 (4), 16 (2013) [J. Math. Sci., 205, 335 (2015)].
2. H. Federer, Geometric Measure
Theory (Springer, New York, 1969).
3. G. B. Folland and E. M. Stein, Hardy Spaces
on Homogeneous Groups (Princeton Univ. Press, Princeton,
1982).
4. B. Franchi and R. Serapioni, “Intrinsic Lipschitz graphs within Carnot
groups,” J. Geom. Anal. 26, 1946
(2016).
5. B. Franchi, R. Serapioni, and F. Serra Cassano, “Rectifiability and perimeter
in the Heisenberg group,” Math. Ann. 321, 479
(1971).