1. G. Bianchi, A. Burchard, P. Gronchi, A. Volčič, private communication.
2. Steiner symmetrals and their distance from a ball;Bianchi;Israel J. Math.,2003
3. A countable set of directions is sufficient for Steiner symmetrization;Bianchi;Adv. in Appl. Math.,2011
4. Theory of Convex Bodies;Bonnesen,1987
5. Estimates related to Steiner symmetrizations;Bourgain,1989