1. Audretsch, J., Bleyer, U., and Lämmerzahl, C. (1993).Phys. Rev. A 47, 4632.
2. Audretsch, J., Hehl, F.-W., and Lämmerzahl, C. (1992). InRelativistic Gravity Research With Emphasis on Experiments and Observations, J. Ehlers and G. Schäfer, eds. (Springer Lecture Notes in Physics 410, Springer-Verlag, Berlin).
3. Audretsch, J., and Lämmerzahl, C. (1991).J. Math. Phys. 32, 1354 (referred to as I).
4. Audretsch, J., and Lämmerzahl, C. (1991).J. Math. Phys. 32, 2099 (referred to as II).
5. Audretsch, J., and Lämmerzahl, C. (1993). InSemantic Aspects of Spacetime Theories, U. Majer, H.-J. Schmidt, eds. (B.I. Wissenschaftsverlag, Mannheim).