1. Propagation in slowly varying waveguides;Bretherton;Proc. Roy. Soc. A,1969
2. Wavetrains in inhomogeneous moving media;Bretherton;Proc. Roy. Soc. A,1969
3. Methods of Mathematical Physics, II;Courant;Interscience,1962
4. The geometrical theory of diffraction;Keller;Proceedings of the Symposium on Microwave Optics, McGill University, 1953 or J. Opt. Soc. Amer.,1962