@article{DAN_1964_156_2_a1,
     author = {M. I. Vishik and G. I. \`Eskin},
     title = {Singular elliptic equations and systems of variable order},
     journal = {Doklady Akademii Nauk},
     pages = {243--246},
     publisher = {mathdoc},
     volume = {156},
     number = {2},
     year = {1964},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1964_156_2_a1/}
}