Submitted on: 14 March 2002.
Revised on: 09 July 2002.
Accepted on: 24 July 2002.
___________________Differential Equations and Dynamical Systems
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Submitted on: 30 November 2019.
Revised on: 25 January 2020.
Accepted on: 25 February 2020.
___________________Differential Equations and Dynamical Systems
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Submitted on: 31 December 2006.
Revised on: 22 February 2007.
Accepted on: 23 April 2007.
___________________Differential Equations and Dynamical Systems
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Submitted on: 25 June 2023.
Revised on: 25 September 2023.
Accepted on: 09 November 2023.
___________________Differential Equations and Dynamical Systems