1. O. Heaviside, Electr. 31, 5125–5134 (1893)
2. W. Pauli, Theory of relativity (Dover publications Inc, New York, 1981)
3. S. Weinberg, Gravitation and cosmology: principles and applications of the general theory of relativity (Wiley and sons, Inc., London, 1972)
4. C.W. Misner, K.S. Thorn, J.A. Wheeler, Gravitation (Princeton University Press, Princeton, 2017)
5. A. Einstein, Sitzungsber. Preuss. Akad. Wiss. Berlin (Math. Phys.), (1915)