1. E. Sanchez-Palencia, Non-Homogeneous Media and Vibration Theory (Springer, Berlin, 1980), p. 409
2. V. Shestopalov, Y.V. Shestopalov, Spectral Theory and Excitation of Open Structures (IET, London, 1996), p. 412
3. A.S. Ilinskii, V.V. Kravtsov, A.G. Sveshnikov, Mathematical Models of Electrodynamics (Vysshaya Shkola, Moscow, 1991), p. 321
4. A.S. Zilbergleit, Y.I. Kopilevich, Spectral Theory of Regular Waveguides (Leningrad: Izd-vo Fiz.-tech. in-ta., 1983) (in Russian)
5. G. Hanson, Yakovlev A Operator Theory for Electromagnetics, 2nd edn. (Springer, Berlin, 2002), p. 653