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Submitted on: 15 December 1999.
Revised on: 05 April 2000.
Accepted on: 01 May 2000.
___________________Hacettepe Journal of Mathematics and Statistics
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Submitted on: 26 April 2004.
Revised on: 17 May 2004.
Accepted on: 28 May 2004.
___________________Hacettepe Journal of Mathematics and Statistics
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Submitted on: 17 September 2001.
Revised on: 25 October 2001.
Accepted on: 23 November 2001.
___________________Hacettepe Journal of Mathematics and Statistics
Submitted on: 14 May 2019.
Revised on: 28 July 2019.
Accepted on: 29 August 2019.
___________________Hacettepe Journal of Mathematics and Statistics
Submitted on: 03 October 1999.
Revised on: 07 November 1999.
Accepted on: 18 November 1999.
___________________Hacettepe Journal of Mathematics and Statistics