@Article{ savtom98, author = { Savaré, Giuseppe and Tomarelli, Franco }, title = { Superposition and Chain Rule for Bounded Hessian Functions }, journal = { Advances in Mathematics }, year = { 1998 }, volume = { 140 }, pages = { 237-281 }, URL = { http://cvgmt.sns.it/paper/930/ }, note = { cvgmt preprint} }