2Ahmad S.On almost periodic solutions of the completing species problems. Journal of the American Mathematical Society . 1998
3Ding T,Zanolin F.Periodic solutions and subharmonic solutions for a class of planar systems of Lotka-Volterra type. Proceedings for the First World Congress of Nonlinear Analysts . 1992
4Hausrath A R,Manasevich R F.Periodic solutions of a periodically perturbed Lotka-Volterra equation using the Poincare-Birkhoff theorem. Journal of Mathematical Analysis and Applications . 1991
5Alvarz C,Lazer A C.An application of topological degree to the periodic competing species problem. Journal of the Australian Mathematical Society . 1986
6Bogoljubov N N,Mitropoliskii Ju A,Samoilenko A M.Methods of Accelerated Convergence inNonlinear Mechanics. . 1976