1. Courant, R., Hilbert, D. Methods of Mathematical Physics, Vol. II, Wiley-Interscience, 1962.
2. Garabedian, P. R. Partial Differential Equations, Wiley, 1964.
3. Hellwig, G. Partial Differential Equations, Blaisdell, 1964.
4. Roubine, E. (Editor). Mathematics Applied to Physics, Springer, 1970.
5. Coulson, C. A., Jeffrey, A. Waves, 2nd Ed. Longman, 1977.