@article{RM_1960_15_1_a0,
     author = {B. M. Levitan and I. S. Sargsyan},
     title = {Some problems in the theory of {a~Sturm--Liouville} equation},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {1--95},
     publisher = {mathdoc},
     volume = {15},
     number = {1},
     year = {1960},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1960_15_1_a0/}
}