《北史·列传·卷八十四》
难敌死了，儿子杨毅承继职位，自称使持节、龙骧将军、左贤王、下辨公；让坚头的儿子做使持节、冠军将军、右贤王、河池公。
难敌死，子毅立。自号使持节、龙骧将军、左贤王、下辨公；以坚头子盘为使持节、冠军将军、右贤王、河池公。
Nandu died, and his son Yang Yi succeeded him, calling himself an envoy with power, the General of the Dragon's Might, the Left Worthy King, and the Duke of Xia Bian. He made Jian Tou's son an envoy with power, the General of the Champion, the Right Worthy King, and the Duke of Hechi.