1. Tidop Research Group, University of Salamanca, Patio de Escuelas 1, E-38008 Salamanca, Spain
2. Department of Computer Science and Artificial Intelligence, University of Alicante, Campus de San Vicente, Ap. Correos 99, E-03080 Alicante, Spain
3. Department of Computer, Catholic University of Ãvila, Calle Canteros, s/n, E-05005 Ãvila, Spain