@article{DE_1983_19_9_a9,
     author = {A. L. Teptin},
     title = {On the question of the sign of the {Green} function},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1542--1547},
     publisher = {mathdoc},
     volume = {19},
     number = {9},
     year = {1983},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1983_19_9_a9/}
}