1. S.L. Sobolev,Partial Differential Equations of Mathematical Physics (Dover, New York, 1964), Lectures 14 and 23.
2. R. Courant and D. Hilbert,Methods of Mathematical Physics, Vol. 1 (Interscience, New York, 1953), p. 314.
3. E. Butkov,Mathematical Physics (Addison-Wesley, Reading, 1968), Chap. 9.
4. H.A. Múnera, D. Buriticá, O. Guzmán, and J.I. Vallejo, “Soluciones no convencionales de la ecuación de ondas viajeras,”Revista Colombiana de Fmsica 27 (1), 215–218 (1995).
5. M. Abramowitz and I.A. Stegun, eds.,Handbook of Mathematical Functions (Dover, New York, 1972).