1. R. A. Adams, Sobolev Spaces, Academic Press (London, 1975).
2. L. Ambrosio, N. Fusco and D. Pallara, Functions of Bounded Variation and Free Discontinuity Problems, Oxford Mathematical Monographs, Oxford University Press (2000).
3. Z. M. Balogh, C. Pintea and H. Rohner, Size of tangencies to non-involutive distributions, Indiana Univ. Math. J., 60 (2011) 2061–2092.
4. I. Chavel, Riemannian Geometry, a Modern Introduction, Cambridge Tracts in Mathematics, vol. 108, Cambridge University Press (1995).
5. S. Delladio, Functions of class C1 subject to a Legendre condition in an enhanced density set, Rev. Mat. Iberoam., 28 (2012), 127–140.