@article{SM_1968_5_2_a5,
     author = {B. M. Levitan},
     title = {Properties of the {Green's} function for a {Sturm--Liouville} equation
},
     journal = {Sbornik. Mathematics},
     pages = {229--259},
     publisher = {mathdoc},
     volume = {5},
     number = {2},
     year = {1968},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1968_5_2_a5/}
}