no. 4
Second order linear differential systems
Annales scientifiques de l'École Normale Supérieure, Série 4, Tome 13 (1980) no. 4, pp. 437-449. 
@article{ASENS_1980_4_13_4_437_0,
     author = {Neuman, F.},
     title = {Second order linear differential systems},
     journal = {Annales scientifiques de l'\'Ecole Normale Sup\'erieure},
     pages = {437--449},
     publisher = {Elsevier},
     volume = {Ser. 4, 13},
     number = {4},
     year = {1980},
     doi = {10.24033/asens.1391},
     zbl = {0453.34006},
     mrnumber = {82d:34053},
     language = {en},
     url = {archive.numdam.org/item/ASENS_1980_4_13_4_437_0/}
}
Neuman, F. Second order linear differential systems. Annales scientifiques de l'École Normale Supérieure, Série 4, Tome 13 (1980) no. 4, pp. 437-449. doi : 10.24033/asens.1391. http://archive.numdam.org/item/ASENS_1980_4_13_4_437_0/

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