@article{1183529395,
author = {Hartman, Philip},
title = {Disconjugate $n$th order differential equations and principal solutions},
journal = {Bull. Amer. Math. Soc.},
volume = {74},
number = {6},
year = {1968},
pages = { 125-129},
language = {en},
url = {http://dml.mathdoc.fr/item/1183529395}
}
Hartman, Philip. Disconjugate $n$th order differential equations and principal solutions. Bull. Amer. Math. Soc., Tome 74 (1968) no. 6, pp. 125-129. http://gdmltest.u-ga.fr/item/1183529395/