1. Bates, R.H.T.: ‘General introduction to the extended boundary condition’, Varadan, V.K., Varadan, V.V., Acoustic, electromagnetic and elastic scattering—focus on the T-matrix approach, (Pergamon Press 1980), p. 21–31
2. Kreysig, E.: Advanced engineering mathematics, (John Wiley and Sons, Inc. 1972)