%0 Journal Article %A V. K. Polishchuk %T On the analytic theory of the equation $z^2u^{''}-f(z)u=0$.~I, II %J Differencialʹnye uravneniâ %D 1972 %P 1999-2011 %V 8 %N 11 %I mathdoc %U http://geodesic.mathdoc.fr/item/DE_1972_8_11_a11/ %G ru %F DE_1972_8_11_a11