@article{DAN_1989_309_6_a9,
     author = {K. B. Sabitov},
     title = {Maximum modulus principles for some classes of second-order},
     journal = {Doklady Akademii Nauk},
     pages = {1321--1324},
     publisher = {mathdoc},
     volume = {309},
     number = {6},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1989_309_6_a9/}
}