Submitted on: 28 November 2001.
Revised on: 03 March 2002.
Accepted on: 16 April 2002.
___________________Cuadernos de Economia---UNIV NAC COLOMBIA, FAC CIENCIAS ECONOMICAS, CUADERNOS ECONOMIA
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Submitted on: 01 August 2000.
Revised on: 16 September 2000.
Accepted on: 03 October 2000.
___________________Cuadernos de Economia---UNIV NAC COLOMBIA, FAC CIENCIAS ECONOMICAS, CUADERNOS ECONOMIA
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Submitted on: 20 August 2017.
Revised on: 17 November 2017.
Accepted on: 08 December 2017.
___________________Cuadernos de Economia---UNIV NAC COLOMBIA, FAC CIENCIAS ECONOMICAS, CUADERNOS ECONOMIA