We consider a large class of retarded functional differential equations subject to impulse effects at variable times, and we present an averaging result for this class of equations by means of the techniques and tools of the theory of generalized ordinary differential equations introduced by J. Kurzweil.
M. Federson. J.G. Mesquita. "Averaging principle for functional differential equations with impulses at variable times via Kurzweil equations." Differential Integral Equations 26 (11/12) 1287 - 1320, November/December 2013. https://doi.org/10.57262/die/1378327427