@article{INTF_1988_32_a1,
     author = {V. A. Kondratiev and E. M. Landis},
     title = {Qualitative theory of second order linear partial differential equations},
     journal = {Itogi Nauki i Tekhniki. Seriya Sovremennye Problemy Matematiki. Fundamental'nye Napravleniya },
     pages = {99--215},
     publisher = {mathdoc},
     volume = {32},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/INTF_1988_32_a1/}
}