@article{1077491737,
author = {Barnett, I. A. and Reingold, H.},
title = {Invariants of a system of linear homogeneous differential
equations of the second order},
journal = {Duke Math. J.},
volume = {6},
number = {1},
year = {1940},
pages = { 141-147},
language = {en},
url = {http://dml.mathdoc.fr/item/1077491737}
}
Barnett, I. A.; Reingold, H. Invariants of a system of linear homogeneous differential
equations of the second order. Duke Math. J., Tome 6 (1940) no. 1, pp. 141-147. http://gdmltest.u-ga.fr/item/1077491737/