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Submitted on: 13 February 2003.
Revised on: 11 April 2003.
Accepted on: 06 May 2003.
___________________CLASSICAL AND QUANTUM GRAVITY---IOP PUBLISHING LTD
Submitted on: 18 July 2020.
Revised on: 05 November 2020.
Accepted on: 18 December 2020.
___________________CLASSICAL AND QUANTUM GRAVITY---IOP PUBLISHING LTD
Submitted on: 18 December 2015.
Revised on: 10 March 2016.
Accepted on: 24 April 2016.
___________________CLASSICAL AND QUANTUM GRAVITY---IOP PUBLISHING LTD
Submitted on: 03 December 2011.
Revised on: 01 April 2012.
Accepted on: 19 April 2012.
___________________CLASSICAL AND QUANTUM GRAVITY---IOP PUBLISHING LTD
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