1. W. F. Ames,Nonlinear Partial Differential Equations in Engineering, Vols. I and II, New York: Academic Press (1965,1972).
2. R. L. Anderson and N. H. Ibragimov,Lie-Bäcklund Transformations in Applications, Philadelphia: SIAM (1979).
3. Yu. Berest, Construction of fundamental solutions for Huygens equations as invariant solutions,Dokl. Akad. Nauk SSSR, 317(4), 786–789 (1991).
4. L. Bianchi,Lezioni sulla teoria dei gruppi continui finiti di trasformazioni, Pisa: Spoerri (1918).
5. G. Birkhoff,Hydrodynamics, Princeton, NJ: Princeton University Press (1950, 1960).