1. AIT DADS E., ARINO O. & EZZINBI K., Almost periodic solution for some nonlinear delay integral equation, J. Nonlinear Times Digest. (To appear.)
2. Periodic solutions to delay differential equations arising in some models of epidemiology;Busenberg,1979
3. A periodicity threshold theorem for epidemics and population growth;Cooke;Math. Biosci.,1976
4. Almost periodic differential equations;Fink;Lecture Notes in Mathematics,1974