1. TIEC Department , University of Mundaiz kalea 50, Donostia 20012 , Spain , inigo.lopez@ehu.eus
2. TIEC Department , University of Mundaiz kalea 50, Donostia 20012 , Spain
3. HiTZ Basque Center for Language Technologies–Ixa NLP Group , University of the Basque Country (UPV/EHU). M. Lardizabal 1, Donostia 20018 , Spain