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Submitted on: 03 September 2014.
Revised on: 27 September 2014.
Accepted on: 23 October 2014.
Moscow University Mechanics Bulletin
Submitted on: 06 July 2017.
Revised on: 17 August 2017.
Accepted on: 11 September 2017.
Moscow University Mechanics Bulletin
Submitted on: 17 December 2012.
Revised on: 14 January 2013.
Accepted on: 22 January 2013.
Moscow University Mechanics Bulletin
Submitted on: 03 November 2015.
Revised on: 09 December 2015.
Accepted on: 06 January 2016.
Moscow University Mechanics Bulletin
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Submitted on: 18 April 2011.
Revised on: 27 April 2011.
Accepted on: 21 May 2011.
Moscow University Mechanics Bulletin
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