@inproceedings{inproceedings946a68ca,
title   = {On periodic solutions of systems of type 'X PONTO' =h(y), 'Y PONTO' =-(f1(x)h1 (y)+f2 (x)h2 (y)+...+Fn (x)hn (y))},
author = {Guidorizzi, Hamilton L.},
year = {1991},
publisher = {Ufrj},
booktitle   = {Seminário Brasileiro de Análise}
}