@Article{ butoudste02, author = { Buttazzo, Giuseppe and Oudet, Edouard and Stepanov, Eugene }, title = { Optimal transportation problems with free Dirichlet regions }, journal = { Progress in Nonlinear Diff. Equations and their Applications }, year = { 2002 }, volume = { 51 }, pages = { 41-65 }, URL = { http://cvgmt.sns.it/paper/494/ }, note = { cvgmt preprint} }