@article{CMH_1961__36_139236,
     author = {I.I, Jr. Hirschman},
     title = {Variation {Diminishing} {Transformations} and {STURM-LIOUVILLE} {Systems.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {214--233},
     publisher = {mathdoc},
     volume = {36},
     year = {1961},
     zbl = {0109.05804},
     url = {http://geodesic.mathdoc.fr/item/CMH_1961__36_139236/}
}