Department of Mathematics and Computer Science, University of the Balearic Islands, Palma, Spain. jairo@uib.es|Department of Mathematics and Computer Science, University of the Balearic Islands, Palma, Spain. jairo@uib.es|Department of Mathematics and Computer Science, University of the Balearic Islands, Palma, Spain. jairo@uib.es|Department of Mathematics and Computer Science, University of the Balearic Islands, Palma, Spain. jairo@uib.es