@article{DE_1988_24_11_a13,
     author = {K. B. Sabitov},
     title = {The maximum principle for equations of mixed type},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1967--1976},
     publisher = {mathdoc},
     volume = {24},
     number = {11},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1988_24_11_a13/}
}