Department of Computer Science and Industrial Engineering, University of Lleida, C/Jaume II 69, E-25001 Lleida, Spain. jrius@diei.udl.cat|Department of Computer Science and Industrial Engineering, University of Lleida, C/Jaume II 69, E-25001 Lleida, Spain. jrius@diei.udl.cat|Department of Computer Science and Industrial Engineering, University of Lleida, C/Jaume II 69, E-25001 Lleida, Spain. jrius@diei.udl.cat|Department of Computer Science and Industrial Engineering, University of Lleida, C/Jaume II 69, E-25001 Lleida, Spain. jrius@diei.udl.cat|Department of Computer Science and Industrial Engineering, University of Lleida, C/Jaume II 69, E-25001 Lleida, Spain. jrius@diei.udl.cat|Department of Computer Science and Industrial Engineering, University of Lleida, C/Jaume II 69, E-25001 Lleida, Spain. jrius@diei.udl.cat