Submitted on: 14 June 1999.
Revised on: 12 July 1999.
Accepted on: 20 July 1999.
Tamkang Journal of Mathematics
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Submitted on: 24 December 2014.
Revised on: 03 February 2015.
Accepted on: 24 February 2015.
Tamkang Journal of Mathematics
Submitted on: 10 June 2000.
Revised on: 06 July 2000.
Accepted on: 28 July 2000.
Tamkang Journal of Mathematics
Submitted on: 05 December 1998.
Revised on: 21 December 1998.
Accepted on: 17 January 1999.
Tamkang Journal of Mathematics
Submitted on: 04 February 1998.
Revised on: 13 March 1998.
Accepted on: 20 March 1998.
Tamkang Journal of Mathematics
Submitted on: 08 February 2000.
Revised on: 12 March 2000.
Accepted on: 22 March 2000.
Tamkang Journal of Mathematics
http://reply.papertrans.cn/3/292/29166/29166-18.png
Submitted on: 17 August 2017.
Revised on: 12 September 2017.
Accepted on: 18 September 2017.
Tamkang Journal of Mathematics
http://reply.papertrans.cn/3/292/29166/29166-20.png