New Book of Tang, vol. 13. His status as co-founder on par with Gaozu appeared certain by the time the Southern Tang, which claimed inheritance of Tang heritage, was established, as its founding emperor Emperor Liezu (Li Bian) recognized that status by treating Emperors Gaozu and Taizong, as well as his adoptive father Xu Wen, all as founders of his state. See Zizhi Tongjian, vol. 282.
