1. Cnops J. (1994) Hurwitz pairs and applications of Möbius transformations, Habilitation Thesis — Ghent, Belgium.
2. Delanghe R., Sommen F. and Soucek V. (1992) Clifford algebras and spinor-valued functions, Kluwer Academic Publishers.
3. Gilbert J. and Murray M. (1991) Clifford algebras and Dirac operators in harmonic analysis, Cambridge University Press.
4. Hochstadt H. (1986) The functions of mathematical physics, Dover Publications, Inc., New York.
5. Huber A. (1954) On the uniqueness of generalized axially symmetric potentials, Annals of Mathematics
60, no.2, September, 351–358.