@Article{ fraserser01, author = { Franchi, Bruno and Serapioni, Raul and Serra Cassano, Francesco }, title = { Rectifiability and Perimeter in the Heisenberg Group }, journal = { Math.Ann. }, year = { 2001 }, volume = { 321 }, pages = { 479-531 }, URL = { http://cvgmt.sns.it/paper/1188/ }, note = { cvgmt preprint} }