Costarelli, Danilo http://orcid.org/0000-0001-8834-8877
Sambucini, Anna Rita http://orcid.org/0000-0003-0161-8729
Funding for this research was provided by:
Istituto Nazionale di Alta Matematica “Francesco Severi”
Dipartimento di Matematica e Informatica dell’Università degli Studi di Perugia
Article History
Received: 11 December 2017
Accepted: 23 January 2018
First Online: 5 February 2018