@Article{ ambkirpra03, author = { Ambrosio, Luigi and Kirchheim, Bernd and Pratelli, Aldo }, title = { Existence of optimal transport maps for crystalline norms }, journal = { Duke Math. J. }, year = { 2004 }, volume = { 125 }, number = { 2 }, pages = { 207-241 }, URL = { http://cvgmt.sns.it/paper/884/ }, note = { cvgmt preprint} }