Department of Mathematics and Computer Science, University of Balearic Islands, ctra. de Valldemossa Km 7.5, Palma de Mallorca, 07122 Spain. emidio.capriotti@uib.es|Department of Mathematics and Computer Science, University of Balearic Islands, ctra. de Valldemossa Km 7.5, Palma de Mallorca, 07122 Spain. emidio.capriotti@uib.es|Department of Mathematics and Computer Science, University of Balearic Islands, ctra. de Valldemossa Km 7.5, Palma de Mallorca, 07122 Spain. emidio.capriotti@uib.es|Department of Mathematics and Computer Science, University of Balearic Islands, ctra. de Valldemossa Km 7.5, Palma de Mallorca, 07122 Spain. emidio.capriotti@uib.es