@article{701746,
     title = {An introduction to spectral and differential geometry in Carnot-Carath\'eodory spaces},
     booktitle = {Proceedings of the 24th Winter School "Geometry and Physics"},
     series = {GDML\_Books},
     publisher = {Circolo Matematico di Palermo},
     address = {Palermo},
     year = {2005},
     pages = {[139]-196},
     mrnumber = {MR2152359},
     zbl = {1105.58012},
     url = {http://dml.mathdoc.fr/item/701746}
}

Rumin, Michael. An introduction to spectral and differential geometry in Carnot-Carathéodory spaces, dans Proceedings of the 24th Winter School "Geometry and Physics", GDML_Books,  (2005), pp. [139]-196. http://gdmltest.u-ga.fr/item/701746/