@article{GDZPPN00247655X, title = {A Generalized Sturm Comparison Theorem and Oscillation Coefficients.}, journal = {Monatshefte f\"ur Mathematik}, volume = {73}, year = {1969}, pages = {207-212}, zbl = {0182.12301}, url = {http://dml.mathdoc.fr/item/GDZPPN00247655X} }
Fink, A.M.; Mary, D.F.St. A Generalized Sturm Comparison Theorem and Oscillation Coefficients.. Monatshefte für Mathematik, Tome 73 (1969) pp. 207-212. http://gdmltest.u-ga.fr/item/GDZPPN00247655X/