@Article{ brafra11, author = { Brasco, Lorenzo and Franzina, Giovanni }, title = { On the Hong-Krahn-Szego inequality for the $p-$Laplace operator }, journal = { Manuscripta Math. }, year = { 2012 }, pages = { 18 }, URL = { http://cvgmt.sns.it/paper/520/ }, note = { cvgmt preprint} }