Jauch, J. M.: Helv. Phys. Acta31, 127 (1958)
Kato, T.: Perturbation theory for linear operators. Chaps. 7, 10. New York: Springer Inc. 1966
Lavine, R.: Indiana Univ. Math. J.21, 643 (1972)
Lavine, R.: J. Functional Anal.12, 30 (1973)
Ziman, J. M.: Electrons and phonons. Chap. VI. London: Oxford University Press 1960
Titchmarsh, E. C.: Eigenfunction expansions, Part II. Chap. XXI. London: Oxford University Press 1958
Dunford, N., Schwartz, J. T.: Linear operators, Part II. Chap. XIII, Sec. 7. New York: Interscience Publishers Inc. 1963
Odeh, F., Keller, J.: J. Math. Phys.5, 1499 (1964)
Scharf, G.: Helv. Phys. Acta39, 556 (1966)
Eastham, M. S. P.: Proc. Roy. Soc. Edinburgh69 A, 125 (1971)
Avron, J., Grossmann, A., Rodriguez, R.: Hamiltonians in the one electron theory of solids I, (preprint, Centre de Physique Théorique, C.N.R.S., Marseille 1972).
Lenahan, T. A.: On quantum mechanical scattering in periodic media. Ph.D. Thesis in Applied Mathematics, Univ. of Pennsylvania, (1970), Chap. IV, (unpublished)
Dunford, N., Schwartz, J. T.: Linear operators, Part I. New York: Interscience Publishers, Inc. 1958