@article{DE_1983_19_4_a22,
     author = {E. G. Zelkin},
     title = {Systems of two second order differential equations and partial differential equations of elliptic type},
     journal = {Differencialʹnye uravneni\^a},
     pages = {700--703},
     publisher = {mathdoc},
     volume = {19},
     number = {4},
     year = {1983},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1983_19_4_a22/}
}