@article{1250129858,
author = {Grasman, William},
title = {Periodic solutions of autonomous differential equations in higher dimensional spaces},
journal = {Rocky Mountain J. Math.},
volume = {7},
number = {4},
year = {1977},
pages = { 457-466},
language = {en},
url = {http://dml.mathdoc.fr/item/1250129858}
}
Grasman, William. Periodic solutions of autonomous differential equations in higher dimensional spaces. Rocky Mountain J. Math., Tome 7 (1977) no. 4, pp. 457-466. http://gdmltest.u-ga.fr/item/1250129858/