1. Project www lingref com document accessed;Somerville;Proceedings October,2017
2. formación de los tiempos compuestos del verbo en español medieval y clásico de filologia de;Garcia Martin,2001
3. Aspect and voice some reflections on perfect and passive In Annie eds Tense aspect New York Academic;Comrie,1981
4. of the Spanish language CUP;Penny;history,1991
5. Verbal periphrases in a Functional Grammar of Spanish de Gruyter;Olbertz,1998