Funding for this research was provided by:
Istituto Nazionale di Alta Matematica "Francesco Severi" (PRIN 2019)
This paper has been supported by the RUDN University Strategic Academic Leadership Program
Università degli Studi di Catania (Dipartimento di Matematica e Informatica)
Article History
Received: 17 November 2020
Accepted: 6 April 2021
First Online: 21 April 2021
Competing interests
: The authors declare that they have no competing interests.