@article{BSMF_1990__118_2_147_0, author = {Xu, Chao-Jiang}, title = {Subelliptic variational problems}, journal = {Bulletin de la Soci\'et\'e Math\'ematique de France}, pages = {147--169}, publisher = {Soci\'et\'e math\'ematique de France}, volume = {118}, number = {2}, year = {1990}, doi = {10.24033/bsmf.2141}, zbl = {0717.49004}, mrnumber = {92b:49008}, language = {en}, url = {http://archive.numdam.org/articles/10.24033/bsmf.2141/} }