@article{DAN_1963_148_6_a7,
     author = {S. A. Pak},
     title = {Sign-preserving conditions for the {Green's} function of a {Sturm--Liouville} problem},
     journal = {Doklady Akademii Nauk},
     pages = {1265--1267},
     publisher = {mathdoc},
     volume = {148},
     number = {6},
     year = {1963},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1963_148_6_a7/}
}