1. Discrete and Continuous Boundary Problems;Atkinson,1964
2. Theory of Ordinary Differential Equations;Coddington,1955
3. Disconjugacy;Coppel,1971
4. Parameterizations of Titchmarsch's m(λ)-functions in the limit circle case;Fulton;Trans. Amer. Math. Soc.,1977
5. Lectures on Ordinary Differential Equations;Hille,1969