@article{GDZPPN002317397,
title = {Uniqueness of Principal Values, Complete Monotonicity of Logarithmic Derivatives of Principal Solutions, and Oscillation Theorems.},
journal = {Mathematische Annalen},
volume = {243},
year = {1979},
pages = {257-282},
zbl = {0387.34031},
url = {http://dml.mathdoc.fr/item/GDZPPN002317397}
}
Hartman, Philip. Uniqueness of Principal Values, Complete Monotonicity of Logarithmic Derivatives of Principal Solutions, and Oscillation Theorems.. Mathematische Annalen, Tome 243 (1979) pp. 257-282. http://gdmltest.u-ga.fr/item/GDZPPN002317397/