@Article{ pra, author = { Pratelli, Aldo }, title = { Equivalence between some definitions for the optimal mass transport problem and for the transport density on manifolds }, journal = { Ann. Mat. Pura Appl. }, year = { 2005 }, volume = { 184 }, number = { 2 }, pages = { 215-238 }, URL = { http://cvgmt.sns.it/paper/124/ }, note = { cvgmt preprint} }