@article{ISU_2015_15_1_a4,
     author = {A. Yu. Duplishcheva},
     title = {About differential operators and matrices of the second order},
     journal = {Izvestiya of Saratov University. Mathematics. Mechanics. Informatics},
     pages = {31--37},
     publisher = {mathdoc},
     volume = {15},
     number = {1},
     year = {2015},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ISU_2015_15_1_a4/}
}