@article{DE_1969_5_6_a14,
     author = {G. N. Zhevlakov and S. A. Pak},
     title = {Conditions for the negativity of the {Green's} function of a {Sturm--Liouville} problem for a second order linear ordinary differential equation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1114--1119},
     publisher = {mathdoc},
     volume = {5},
     number = {6},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1969_5_6_a14/}
}