1. On almost periodic solutions for undamped systems with almost periodic forcing;Seifert;Proc Am Math Soc,1972
2. On almost periodic solutions for nonlinear systems with almost periodic forcing;Chongyou;Ann Differ Eqs,1987
3. Almost periodic solution by the method of averaging;Seifert,1973
4. Almost periodic differential equations;Fink,1974
5. Almost periodic differential equations;Chongyou,1992