Fonda, AlessandroKlun, GiulianoSfecci, Andrea2020-05-042020-05-042020-05https://openscience.sissa.it/handle/1963/35349We prove the existence of periodic solutions of some infinite-dimensional systems by the use of the lower/upper solutions method. Both the well-ordered and non-well-ordered cases are treated, thus generalizing to systems some well established results for scalar equations.enPreprintperiodic solutions; lower and upper solutions; degree theory; infinite-dimensional dynamical systems