@article{1183527306,
author = {Birkhoff, Garrett and Kotin, Leon},
title = {Essentially positive systems of linear differential equations},
journal = {Bull. Amer. Math. Soc.},
volume = {71},
number = {6},
year = {1965},
pages = { 771-772},
language = {en},
url = {http://dml.mathdoc.fr/item/1183527306}
}
Birkhoff, Garrett; Kotin, Leon. Essentially positive systems of linear differential equations. Bull. Amer. Math. Soc., Tome 71 (1965) no. 6, pp. 771-772. http://gdmltest.u-ga.fr/item/1183527306/