A. Perez. (2004)cite arxiv:gr-qc/0409061
Comment: Lectures presented at the II International Conference of Fundamental
Interactions, Pedra Azul, Brazil, June 2004. Typos corrected.
R. MacKenzie. (2000)cite arxiv:quant-ph/0004090
Comment: 55 pages, 23 figures. Lectures given at Rencontres du Vietnam: VIth
Vietnam School of Physics, Vung Tau, Vietnam, 27 December 1999 - 8 January
2000.