Periodic Solutions of Complex-Valued Differential Equations and Systems with Periodic Coefficients*

has been considered by Srzednicki [11 13], using a combination of generalized Conley's isolating blocks, the index of singular points of autonomous systems and the Lefschetz fixed point theorem. Recently, it has been shown that slight extensions of Srzednicki's results could be obtained in a simpler and more elementary way using continuation theorems of the Leray Schauder type (see [6, 9]). The aim of the present paper is to show that the same methodology can be adapted to prove the existence of periodic solutions for more general classes of equations and systems. article no. 0054