@article{1077492258, author = {Levine, Jack}, title = {Invariants of systems of second order linear differential equations}, journal = {Duke Math. J.}, volume = {6}, number = {1}, year = {1940}, pages = { 298-311}, language = {en}, url = {http://dml.mathdoc.fr/item/1077492258} }
Levine, Jack. Invariants of systems of second order linear differential equations. Duke Math. J., Tome 6 (1940) no. 1, pp. 298-311. http://gdmltest.u-ga.fr/item/1077492258/