no. 3
Comportement semi-classique du spectre des hamiltoniens quantiques hypoelliptiques
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 9 (1982) no. 3, pp. 405-431. 
@article{ASNSP_1982_4_9_3_405_0,
     author = {Helffer, Bernard and Robert, Didier},
     title = {Comportement semi-classique du spectre des hamiltoniens quantiques hypoelliptiques},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {405--431},
     publisher = {Scuola normale superiore},
     volume = {4e s{\'e}rie, 9},
     number = {3},
     year = {1982},
     zbl = {0507.35066},
     mrnumber = {681933},
     language = {fr},
     url = {archive.numdam.org/item/ASNSP_1982_4_9_3_405_0/}
}
Helffer, B.; Robert, D. Comportement semi-classique du spectre des hamiltoniens quantiques hypoelliptiques. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 9 (1982) no. 3, pp. 405-431. http://archive.numdam.org/item/ASNSP_1982_4_9_3_405_0/

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