K. Lake. (2004)cite arxiv:astro-ph/0404319
Comment: Final form to appear in Physical Review Letters. Further information
at http://grtensor.org/Robertson/.
D. Hogg. (1999)cite arxiv:astro-ph/9905116
Comment: This short and purely pedagogical text is not submitted anywhere but
here. Errors reported to the author will be rewarded with gratitude and
acknowledgements.