1. F. V. Atkinson, Discrete and Continuous Boundary Value Problems, Academic Press, New York, 1964.
2. F. Brauer, Spectral theory for linear systems of differential equations, Pacific J. Math. 10 (1960), 17–34.
3. E. A. Coddington and N. Levinson, Theory of Ordinary Differential Equations, McGraw-Hill, New York, 1955.
4. D. B. Hinton and J. K. Shaw, Titchmarsh-Weyl theory for Hamiltonian Systems, Spectral Theory of Differential Operations, ed. I. W. Knowles and R. T. Lewis, North Holland.
5. J. K. Shaw —, On the spectrum of a singular Hamiltonian system, Quaes. Math. 5 (1982), 29–81.