Titsingh, p. 114., p. 114, at Google Books; Brown, Delmer et al. (1979). The Future and the Past, p. 285; n.b., Yoshifusa was the first minister to be promoted to Daijō-daijin. That high office was previously filled by Imperial Princes only.
Kimoto, Yoshinobu (2004). "『牛屋大臣』藤原是公について" [On "Ushiya-Daijin" Fujiwara no Korekimi]. 奈良時代の藤原氏と諸氏族 [The Fujiwara Clan and Other Clans of the Nara Period] (in Japanese). Ohfu.
Brinkley, Frank and Dairoku Kikuchi. (1915). A History of the Japanese People from the Earliest Times to the End of the Meiji Era. New York: Encyclopædia Britannica. OCLC 413099
