@article{119991, author = {Jaroslav Krbi\v la}, title = {A note on the definiteness of the differential equations $y'' = q(t)y$}, journal = {Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica}, volume = {12}, year = {1972}, pages = {19-22}, zbl = {0412.34019}, mrnumber = {0379949}, language = {en}, url = {http://dml.mathdoc.fr/item/119991} }
Krbiľa, Jaroslav. A note on the definiteness of the differential equations $y'' = q(t)y$. Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica, Tome 12 (1972) pp. 19-22. http://gdmltest.u-ga.fr/item/119991/
Lineare Differentialtransformationen 2. Ordnung, VEB Deutscher Verlag der Wissenschaften Berlin 1967. (1967) | MR 0236448
Rýdzo diskonjugované homogénne lineárne diferenciálne rovnice druhého rádu, Časopis pro pěstování matematiky (to appear).