@Article{ MazPra17, author = { Mazzoleni, Dario and Pratelli, Aldo }, title = { Some estimates for the higher eigenvalues of sets close to the ball }, journal = { J. Spectral Theory }, year = { 2019 }, pages = { }, URL = { http://cvgmt.sns.it/paper/3421/ }, note = { cvgmt preprint} }