Infinitely many periodic solutions to delay differential equations via critical point theory (Q2015705)

Summary: By the critical point theory, infinitely many \(4\sigma\)-periodic solutions are obtained for the system of delay differential equations \[ \dot{x}(t)=-f(x(t-\sigma)), \] where \(\sigma\in(0,+\infty)\) and \(f\in C(\mathbb R^n, \mathbb R^n)\).