@article{SVFU_2021_28_3_a1,
     author = {A. I. Kozhanov and G. A. Lukina},
     title = {Degeneration in differential equations with multiple characteristics},
     journal = {Matemati\v{c}eskie zametki SVFU},
     pages = {19--30},
     year = {2021},
     volume = {28},
     number = {3},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/SVFU_2021_28_3_a1/}
}