1. H. Weyl:Sitzungsber. Preuss. Akad. Wiss. (1918), p. 465.
2. P. G. Bergmann:Introduction to the Theory of Relativity (Englewood Cliffs, N.J., 1942).
3. T. Y. Thomas:Concepts from Tensor Analysis and Differential Geometry, 2nd Edition (New York and London, 1965)
4. I. S. Sokolnikoff:Tensor Analysis, 2nd Edition (New York, London, Sydney, 1964).
5. G. Møller:The Theory of Relativity (London, 1952).