1. A Continuous Analogue of Sturm Sequences in the Context of Sturm–Liouville Equations
2. : Direct Methods of the Qualitative Spectral Analysis of Singular Differential Operators, Fizmatgiz, Moscow, 1963 (Russian)
3. : Lecture Notes on Ideal Magnetohydrodynamics, Rijnhuizen Report, Fom-Instituut voor Plasmafysica, Nieuwegein, 83–145, 1983