“…Oscillatory properties of eigenfunctions and basis properties in various functional spaces of root functions of Sturm-Liouville problems with a spectral parameter in the boundary conditions were investigated in [1, 3, 4, 11, 15–18, 21, 24, 26–28, 31, 34, 36–38, 40]. These properties of the root functions of eigenvalue problems for ordinary differential equations of the fourth order, one of the boundary conditions of which depends on the spectral parameter, were studied in detail in [2, 12, 13, 22, 23, 29, 30, 32, 33, 39]. In the case when two of the boundary conditions contain a spectral parameter, these problems were studied in [5, 6, 9, 10, 32], and when three of the boundary conditions contain a spectral parameter, they were studied in [8].…”