1. N.I. Akhiezer, The Classical Moment Problem, Oliver and Boyd, Edinburgh and London, 1965 (translated from the Russian edition of 1961.
2. N.I. Akhiezer, I.M. Glazman, Theory of Linear Operators in Hilbert Space: I and II. Pitman, London and Scottish Academic Press, Edinburgh, 1981.
3. Discrete and Continuous Boundary Problems;Atkinson,1965
4. C. Bennewitz, The Titchmarsh eigenfunction expansion theory and the m-coefficient, unpublished manuscript, 1983.
5. C. Bennewitz, W.N. Everitt, Some remarks on the Titchmarsh–Weyl m-coefficient, Tribute to Äke Pleijel: Proceedings of the Pleijel Conference, University of Uppsala, 1979, 49–108. Department of Mathematics, University of Uppsala, Sweden, 1979, pp. 49–108.