@article{GDZPPN002057891,
title = {Variation Diminishing Transformations and STURM-LIOUVILLE Systems.},
journal = {Commentarii mathematici Helvetici},
volume = {35},
year = {1961},
pages = {214-233},
zbl = {0109.05804},
url = {http://dml.mathdoc.fr/item/GDZPPN002057891}
}
Hirschman, I.I, Jr. Variation Diminishing Transformations and STURM-LIOUVILLE Systems.. Commentarii mathematici Helvetici, Tome 35 (1961) pp. 214-233. http://gdmltest.u-ga.fr/item/GDZPPN002057891/