@Misc{ areser08, author = { Arena, Gabriella and Serapioni, Raul }, title = { Intrinsic regular submanifolds in Heisenberg groups are differentiable graphs }, journal = { Calc.Var. and PDE }, year = { 2008 }, pages = { }, URL = { http://cvgmt.sns.it/paper/619/ }, note = { cvgmt preprint} }