@misc{misc07fef22a,
title   = {On periodic solutions of systems of the type 'X 2 PONTOS' = h(y),'Y PONTO' = -'N SOBRE SOMATORIA SOBRE I'=1 'F IND.I' (x)'H IND.I' (y)-g (x)},
author = {Guidorizzi, Hamilton L.},
year = {1995},
publisher = {IME-USP}
}