@article{10_4064_sm_139_3_213_244,
     author = {Daniele Morbidelli},
     title = {Fractional {Sobolev} norms and structure of {Carnot-Carath\'eodory} balls for {H\"ormander} vector fields},
     journal = {Studia Mathematica},
     pages = {213--244},
     publisher = {mathdoc},
     volume = {139},
     number = {3},
     year = {2000},
     doi = {10.4064/sm-139-3-213-244},
     language = {fr},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/sm-139-3-213-244/}
}