@article{DE_1972_8_11_a11,
     author = {V. K. Polishchuk},
     title = {On the analytic theory of the equation $z^2u^{''}-f(z)u=0${.~I,} {II}},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1999--2011},
     publisher = {mathdoc},
     volume = {8},
     number = {11},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1972_8_11_a11/}
}