1. W. Rudin, Real and complex analysis, 3rd Ed., McGraw-Hill, New York, 1987.
2. P. Mattila, Geometry of Sets and Measures in Euclidean Spaces, Cambridge Stud. Adv. Math. 44, Cambridge Univ. Press, Cambridge, 1995.
3. N. Alon and J. H. Spencer, The Probabilistic Method, 2nd ed., Wiley-Intersci. Ser. Discrete Math. Optim., Wiley, New York, 2000.
4. V. Aversa and D. Preiss, Hearts density theorems, Real Anal. Exchange 13 (1987), 28–32.
5. —, Sistemi di derivazione invarianti per affinita, preprint, Complesso Universitario di Monte S. Angelo, Napoli, 1995.