“…A good investigation of such sets is undoubtedly necessary for a better understanding of the flows or semiflows they describe (see [20,31,32] for recent developments). Especially when the coefficients of the non-autonomous equation exhibit some recurrent variation in time t, its solutions define a skew-product semiflow in a natural way which permits the analysis of the dynamical properties of the trajectories using methods of topological dynamics and ergodic theory [25,28,30,32,35].…”