On the boundedness of solutions of a certain fourth-order nonlinear differential equation.
(English).Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica,
 Andres J.: Boundedness of solutions of the third order differential equation with oscillatory restoring and forcing terms. Czech. Math. Journal, V.36 111, No. 1, Praha 1986. MR 0822859 | Zbl 0608.34039
 Vlček V.: A note to a certain nonlinear differential equation of the third order. ACTA UP Olom., F.R.N. Math. XXVII, Vol.91, 1988. MR 1039894 | Zbl 0725.34034