@article{1102784209, author = {Bates, P. W. and Ward, J. R.}, title = {Periodic solutions of higher order systems.}, journal = {Pacific J. Math.}, volume = {85}, number = {2}, year = {1979}, pages = { 275-282}, language = {en}, url = {http://dml.mathdoc.fr/item/1102784209} }
Bates, P. W.; Ward, J. R. Periodic solutions of higher order systems.. Pacific J. Math., Tome 85 (1979) no. 2, pp. 275-282. http://gdmltest.u-ga.fr/item/1102784209/