Submitted on: 21 March 2015.
Revised on: 16 May 2015.
Accepted on: 17 June 2015.
___________________Electronic Journal of Differential Equations
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Submitted on: 27 May 2019.
Revised on: 31 August 2019.
Accepted on: 28 September 2019.
___________________Electronic Journal of Differential Equations
Submitted on: 10 August 2007.
Revised on: 23 November 2007.
Accepted on: 25 December 2007.
___________________Electronic Journal of Differential Equations
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Submitted on: 26 January 2020.
Revised on: 25 February 2020.
Accepted on: 14 March 2020.
___________________Electronic Journal of Differential Equations
Submitted on: 27 February 1999.
Revised on: 01 June 1999.
Accepted on: 14 June 1999.
___________________Electronic Journal of Differential Equations
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Submitted on: 01 December 2020.
Revised on: 11 March 2021.
Accepted on: 30 March 2021.
___________________Electronic Journal of Differential Equations