@article{JEDP_1976____A13_0,
     author = {Pham The Lai},
     title = {Th\'eorie spectrale d'une classe d'op\'erateurs diff\'erentiels hypoelliptiques},
     journal = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {13},
     pages = {1--59},
     publisher = {Ecole polytechnique},
     year = {1976},
     language = {fr},
     url = {http://www.numdam.org/item/JEDP_1976____A13_0/}
}