References for Sancho Fernandez
E. Brandenburg: Die Nachkommen Karls des Grossen. Leipzig 1936, Frankfurt 1964
L. de Salazar y Castro: Historia Genealogica de la Casa de Lara. Madrid, 1696, Vol1, p.#
S.de Vajay: From Alfonso VII to Alfonso X - The first two Centuries of the Burgundian Dynasty in Castile and Leon. 1989