@article{VMUMM_1990_2_a17,
     author = {Nguen Min' Chi},
     title = {Fourth-order hypoelliptic pseudodifferential operators with a noninvolutive characteristic set},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {71--73},
     publisher = {mathdoc},
     number = {2},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1990_2_a17/}
}