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Submitted on: 01 November 2016.
Revised on: 03 February 2017.
Accepted on: 02 March 2017.
___________________International Journal of Mathematics for Industry
Submitted on: 19 June 2011.
Revised on: 14 September 2011.
Accepted on: 07 November 2011.
___________________International Journal of Mathematics for Industry
Submitted on: 13 October 2000.
Revised on: 22 December 2000.
Accepted on: 24 January 2001.
___________________International Journal of Mathematics for Industry