1. On an eigenfunction expansion for a fourth-order singular differential equation;Chaudhuri;Quart. J. Math. (Oxford),1969
2. Theory of Ordinary Differential Equations;Coddington,1955
3. On the strong limit-n classification of linear ordinary differential expressions of order 2n;Everitt,1974
4. Direct Methods for the Qualitative Spectral Analysis of Singular Differential Operators;Glazman,1965
5. Limit point criteria for differential equations, II;Hinton;Can. J. Math.,1974