Author: Piazza Aldo Moro 2 00133 Roma, Italy e-mail: deconcini@mat.uniroma1.it Persi Diaconis Department of Statistics Stanford University Stanford, CA 94305-4065, USA e-mail: diaconis@math.stanford.edu, tagaman@stat.stanford.edu Nicola Fusco Dipartimento di Matematica e Applicazioni Universit di Napoli