1. F Catoni, D Boccaletti, R Cannata, V Catoni, E Nichelatti and P Zampetti, The mathematics of Minkowski space-time: with an introduction to commutative hypercomplex numbers (Springer Science & Business Media, 2008)
2. L Corry, Arch. Hist. Exact Sci. 51, 273 (1997)
3. B Koberlein and D Meisel, Astrophysics through computation: With mathematica®support (Cambridge University Press, 2013)
4. C W Misner, K S Thorne and J A Wheeler, Gravitation (WH Freeman and Co., San Francisco, 1973) p 660
5. D J Griffiths, Introduction to electrodynamics (American Association of Physics Teachers, 2005)