Kobza, Jiří:
Zur Bestimmung der Grundintegrale von Differentialgleichung $y''=q(x)y$.
(German) [On determination of basic integrals of differential equation $y''=q(x)y$].Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica-Physica-Chemica,
vol. 12
(1972),
issue 1,
pp. 23-33