Ubarretxena, Aitor (23 February 2013). "Hasier Arraiz, elegido primer presidente de Sortu" [Hasier Arraiz, chosen to be the first president of Sortu]. El Periódico (in Spanish). San Sebastián. Retrieved 9 May 2020.
elperiodicoextremadura.com
Ubarretxena, Aitor (23 February 2013). "Hasier Arraiz, elegido primer presidente de Sortu" [Hasier Arraiz, chosen as the first president of Sortu]. El Periódico Extremadura (in Spanish). Retrieved 9 May 2020.
"Elecciones al Parlamento Vasco 2012 – Comunidad Autónoma de Euskadi"(XLS/CSV). opendata.euskadi.eus (in Spanish). Basque Government. 11 May 2012. Retrieved 9 May 2020. Relevant information is contained within the final electoral lists, which you can find in the archive file "ElecP12_c.xls".
"Lanzan nuevo partido vasco en España" [A new Basque political party is launched in Spain]. Yahoo News (in Spanish). Associated Press. 23 February 2013. Retrieved 9 May 2020.