Submitted on: 18 May 1998.
Revised on: 09 July 1998.
Accepted on: 08 August 1998.
___________________JOURNAL OF PURE AND APPLIED ALGEBRA
Submitted on: 06 April 2012.
Revised on: 21 May 2012.
Accepted on: 10 June 2012.
___________________JOURNAL OF PURE AND APPLIED ALGEBRA
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