Submitted on: 09 September 2000.
Revised on: 19 December 2000.
Accepted on: 09 January 2001.
___________________Carpathian Journal of Mathematics
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Submitted on: 15 February 2019.
Revised on: 03 June 2019.
Accepted on: 16 July 2019.
___________________Carpathian Journal of Mathematics
Submitted on: 02 September 2002.
Revised on: 09 November 2002.
Accepted on: 14 December 2002.
___________________Carpathian Journal of Mathematics
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http://reply.papertrans.cn/1/49/4804/4804-16.png
Submitted on: 06 May 2014.
Revised on: 25 July 2014.
Accepted on: 01 September 2014.
___________________Carpathian Journal of Mathematics
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http://reply.papertrans.cn/1/49/4804/4804-19.png
Submitted on: 27 August 1998.
Revised on: 08 November 1998.
Accepted on: 31 December 1998.
___________________Carpathian Journal of Mathematics