@article{AIF_1980__30_2_109_0,
     author = {Sj\"ostrand, Johannes},
     title = {On the eigenvalues of a class of hypo-elliptic operators. {IV}},
     journal = {Annales de l'Institut Fourier},
     pages = {109--169},
     publisher = {Institut Fourier},
     address = {Grenoble},
     volume = {30},
     number = {2},
     year = {1980},
     doi = {10.5802/aif.788},
     zbl = {0417.47024},
     language = {en},
     url = {https://aif.centre-mersenne.org/articles/10.5802/aif.788/}
}