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Submitted on: 19 June 2003.
Revised on: 30 June 2003.
Accepted on: 20 July 2003.
Proceedings of the Institute of Mathematics and Mechanics
Submitted on: 11 August 2009.
Revised on: 25 August 2009.
Accepted on: 16 September 2009.
Proceedings of the Institute of Mathematics and Mechanics
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