Amster, P., Epstein, J. and Sanjuán Cuéllar, A. 2021. Periodic solutions for systems of functional-differential semilinear equations at resonance. Topological Methods in Nonlinear Analysis. 58, 2 (Dec. 2021), 591–607. DOI:https://doi.org/10.12775/TMNA.2020.078.