References
Jürgen Ehlers
Einstein's theory of gravitation
1979
in: Einstein Symposion Berlin, Dordrecht : Springer
The nature and structure of spacetime
1973
in: The physicist's conception of nature, Dordrecht : Springer
1979
in: Einstein Symposion Berlin, Dordrecht : Springer
1973
in: The physicist's conception of nature, Dordrecht : Springer