1. C. Castro and M. Pavsic, Progress in Physics vol 1 (April 2005) 31.
2. C. Castro, Foundations of Physics 35, no.6 (2005) 971. Prog. in Phys. 1 (April 2005) 20.
3. D. Hestenes, Spacetime Algebra. Gordon and Breach, New York, 1996.
4. M. Pavsic, The Landscape of Theoretical Physics: A Global View, from point particles to the brane world and beyond, in search of a Unifying Principle. (Fundamental Theories of Physics, vol. 19, Kluwer Academic Publishers, Dordrecht, Boston, London, 2001).
5. M. Pavsic, Int. J. Mod. Phys. A 21 (2006) 5905.