Institution: | (1) Institute of Mathematics, Silesian University, Bankowa 14, 40-007 Katowice, Poland;(2) Dipartimento di Matematica Pura ed Applicata, Università di LAquila, Via Vetoio, 67100 LAquila, Italy;(3) Institute of Mathematics, Silesian University and Polish Academy of Science, Bankowa 14, 40-007, Poland |