Multiple solutions for an asymptotically linear wave equation. (Q5933747)

This paper is devoted to multiplicity results for periodic solutions of the wave equation NEWLINE\[NEWLINEu_{tt}-u_{xx}= f(t,x,u),\;0<c<\pi,\;t\in\mathbb{R} \tag{1}NEWLINE\]NEWLINE satisfying boundary and periodicity conditions. Under some natural conditions on the nonlinearity \(f\), the author shows existence of at least three solutions on the non-equivariant case and provides an estimate for the number of periodic solutions of (1), when an action of \(\mathbb{Z}_2\) is involved.