Systems of functional-differential equations periodic solutions for systems of functional-differential semilinear equations at resonance
Motivated by Lazer-Leach type results, we study the existence of periodic solutions for systems of functional-differential equations at resonance with an arbitrary even-dimensional kernel and linear deviating terms involving a general delay of the form $\int_0^{2π}u(t+s)\,dλ(s)$, where $λ$ is a finite regular signed measure. Our main technique shall be the Coincidence Degree Theorem due to Mawhin.
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