《北史·本记·卷二》
赫连定西逃之后，杨难当私占上圭阝。秋七月初一，命令乐平王丕等讨伐他。
赫连定之西也，杨难当窃据上邽，秋七月庚戌，命乐平王丕等讨之。
After Helü Deng Dingxi escaped, Yang Nanddang occupied Shanggusi without authority. At the beginning of the first day of Qiuyue, orders were given to Prince Le Ping Pi and others to attack him.