Submitted on: 25 August 2014.
Revised on: 23 September 2014.
Accepted on: 16 October 2014.
___________________CUBO-A Mathematical Journal---UNIV FRONTERA, DEPT MATEMATICA & ESTADISTICA
Submitted on: 22 December 2019.
Revised on: 01 February 2020.
Accepted on: 14 March 2020.
___________________CUBO-A Mathematical Journal---UNIV FRONTERA, DEPT MATEMATICA & ESTADISTICA
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Submitted on: 11 January 2002.
Revised on: 12 April 2002.
Accepted on: 06 May 2002.
___________________CUBO-A Mathematical Journal---UNIV FRONTERA, DEPT MATEMATICA & ESTADISTICA
Submitted on: 04 November 2005.
Revised on: 17 January 2006.
Accepted on: 25 February 2006.
___________________CUBO-A Mathematical Journal---UNIV FRONTERA, DEPT MATEMATICA & ESTADISTICA
Submitted on: 13 July 2023.
Revised on: 10 September 2023.
Accepted on: 18 October 2023.
___________________CUBO-A Mathematical Journal---UNIV FRONTERA, DEPT MATEMATICA & ESTADISTICA