@article{MZM_1998_64_5_a18,
     author = {M. K. Chernishov},
     title = {Invertibility of first-order linear differential operators},
     journal = {Matemati\v{c}eskie zametki},
     pages = {796--800},
     publisher = {mathdoc},
     volume = {64},
     number = {5},
     year = {1998},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1998_64_5_a18/}
}