Submitted on: 28 August 2021.
Revised on: 25 October 2021.
Accepted on: 21 December 2021.
___________________Collectanea Mathematica---SPRINGER-VERLAG ITALIA SRL
Submitted on: 07 October 2008.
Revised on: 26 January 2009.
Accepted on: 14 March 2009.
___________________Collectanea Mathematica---SPRINGER-VERLAG ITALIA SRL
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Submitted on: 12 November 2008.
Revised on: 25 December 2008.
Accepted on: 09 February 2009.
___________________Collectanea Mathematica---SPRINGER-VERLAG ITALIA SRL
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Submitted on: 16 May 2014.
Revised on: 06 June 2014.
Accepted on: 26 July 2014.
___________________Collectanea Mathematica---SPRINGER-VERLAG ITALIA SRL
Submitted on: 05 August 2012.
Revised on: 02 November 2012.
Accepted on: 27 November 2012.
___________________Collectanea Mathematica---SPRINGER-VERLAG ITALIA SRL
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