Submitted on: 28 March 2010.
Revised on: 14 April 2010.
Accepted on: 06 May 2010.
Tsukuba Journal of Mathematics
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http://reply.papertrans.cn/4/301/30002/30002-33.png
Submitted on: 16 May 1998.
Revised on: 25 June 1998.
Accepted on: 30 June 1998.
Tsukuba Journal of Mathematics
Submitted on: 15 February 2005.
Revised on: 05 March 2005.
Accepted on: 14 March 2005.
Tsukuba Journal of Mathematics
Submitted on: 14 February 2016.
Revised on: 18 March 2016.
Accepted on: 05 April 2016.
Tsukuba Journal of Mathematics