Affiliation: | 1. Department of Mathematics and Computer Science, University of Perugia, Perugia, Italy.danilo.costarelli@unipg.ithttps://orcid.org/0000-0001-8834-8877;3. Department of Mathematics and Computer Science, University of Perugia, Perugia, Italy.https://orcid.org/0000-0002-9875-2790 |