S. Hossenfelder. (2006)cite arxiv:gr-qc/0612167
Comment: replaced with published version. due to page limits this version is
significantly shorter than the 1st.
P. Tuckey. (1993)cite arxiv:gr-qc/9303011
Comment: 5 pages (plus one figure not included, available from author on
request), Plain Tex, no local preprint number (Only change: omitted
"\magnification" command now replaced).