[1] Univ Coimbra, Inst Syst & Robot, P-3030290 Coimbra, Portugal
[2] Cardinal Stefan Wyszynski Univ, Fac Math & Nat Sci, PL-01815 Warsaw, Poland
[3] Univ Tras Os Montes & Alto Douro UTAD, Dept Math, P-5001801 Vila Real, Portugal
[4] Univ Coimbra, Dept Math, P-3001454 Coimbra, Portugal