@article{ERAAMS_2003_09_a13,
     author = {Agrachev, A. and Marigo, A.},
     title = {Nonholonomic tangent spaces: intrinsic construction and rigid dimensions},
     journal = {Electronic research announcements of the American Mathematical Society},
     pages = {111--120},
     publisher = {mathdoc},
     volume = {09},
     year = {2003},
     doi = {10.1090/S1079-6762-03-00118-5},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S1079-6762-03-00118-5/}
}