@article{702374,
     title = {Differential equations, higher monotonicity and principal pair of solutions},
     booktitle = {Equadiff 7},
     series = {GDML\_Books},
     publisher = {BSB B.G. Teubner Verlagsgesellschaft},
     address = {Leipzig},
     year = {1990},
     pages = {139-142},
     zbl = {0718.34045},
     url = {http://dml.mathdoc.fr/item/702374}
}

Vosmanský, J. Differential equations, higher monotonicity and principal pair of solutions, dans Equadiff 7, GDML_Books,  (1990), pp. 139-142. http://gdmltest.u-ga.fr/item/702374/