@Misc{ cappautys, author = { Capogna, Luca and Pauls, Scott and Tyson, Jeremy }, title = { Convexity and a horizontal second fundamental form for hypersurfaces in Carnot groups }, journal = { }, year = { 2006 }, pages = { }, URL = { http://cvgmt.sns.it/paper/1596/ }, note = { cvgmt preprint} }