@article{DE_1988_24_6_a25,
     author = {A. L. Teptin},
     title = {A new condition for the sign-constancy of the {Green} function},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1066--1069},
     publisher = {mathdoc},
     volume = {24},
     number = {6},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1988_24_6_a25/}
}