[1] M. Biernacki: Sur l’equation differentielle $y^{(4)} + A(x)y = 0$. Ann. Univ. Mariae Curie-Skłodowska 6 (1952), 65–78. MR 0064230

[2] S. P. Hastings and A. C. Lazer: On the asymptotic behavior of solutions of the differential equation $y^{(4)} = p(x)y$. Czechoslovak Math.  J. 18(93) (1968), 224–229. MR 0226110

[3] G. D. Jones: Asymptotic behavior of solutions of a fourth order linear differential equation. Czechoslovak Math. J. 38(113) (1988), 578–584. MR 0962901 | Zbl 0672.34052

[4] G. D. Jones: Oscillatory solutions of a fourth order linear differential equation. Lecture notes in pure and apllied Math. Vol 127, 1991, pp. 261–266. MR 1096762

[5] M. K. Kwong and A. Zettl: Norm Inequalities for Derivatives and Differences. Lecture notes in Mathematics, 1536. Springer-Verlag, Berlin, 1992. MR 1223546

[6] M.  Švec: Sur le comportement asymtotique des intégrales de l’équation differentielle $y^{(4)} + Q(x)y = 0$. Czechoslovak Math. J. 8(83) (1958), 230–245. MR 0101355