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Submitted on: 18 June 1999.
Revised on: 15 July 1999.
Accepted on: 02 September 1999.
___________________JOURNAL OF MATHEMATICAL ECONOMICS
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Submitted on: 11 September 2021.
Revised on: 24 November 2021.
Accepted on: 15 December 2021.
___________________JOURNAL OF MATHEMATICAL ECONOMICS
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