1. GRIAL Research Group, Department of Computer and Automatics, University of Salamanca, IUCE, Paseo de Canalejas 169, 37008, Salamanca, Spain
2. GATE, Technical University of Madrid, Calle Ramiro de Maeztu. 7, 1st floor (Rectorado A), 28040 Madrid, Spain
3. GRIAL Research Group, Department of Computer and Automatics Research Institute for Educational Sciences (IUCE), University of Salamanca, Paseo de Canalejas 169, 37008, Salamanca, Spain
4. Technical University of Madrid, Calle Alenza no. 4, office 718, (M Building) 7th floor, 28003, Madrid, Spain
5. Department of Computer and Automatics, Faculty of Sciences, University of Salamanca, Plaza de los Caídos s/n 37008, Salamanca, Spain