1. C hurchill R . V. 1941 Fourier series and boundary value problems. N ew Y o rk : M cGraw -H ill.
2. C o u ran t R . & H ilb e rt D . 1963 Methods of mathematical physics. N ew Y o rk : In terscience.
3. Commun. Pure A ppl;Math.,1961
4. Proc. Roy;Soc. A,1962
5. 6 Proc. Roy;Soc. A,1962