Invariant tori for a reversible oscillator with a nonlinear damping and periodic forcing term

In this paper, the boundedness of all solutions of the oscillator

x^″+f(x,x^′)+ω²x+?(x)=p(t)$x^{″}+f(x,x^{\prime })+{\omega }^{2}x+?(x)=p(t)$

is discussed, where ω$\omega$ is a positive constant, f(x,y),?(x)$f(x,y),?(x)$ and p(t)$p(t)$ are smooth functions, and p(t)=p(t+2π).$p(t)=p(t+2\pi ).$