also forced Cui's secretary Kang Dan (康湛) into forging a letter from Cui to Zhu, offering to betray Fengtian to him. Lu, presenting the forgery to Emperor Dezong, thus falsely accused Cui of treason. Emperor Dezong believed Lu's accusations and executed Cui. Zhu soon put Fengtian under siege. A Tang aid force, commanded by the generals Du Xiquan (杜希全), Dai Xiuyan (戴休顏), Shi Changchun (時常春), and Li Jianhui (李建徽), was approaching Fengtian and requesting imperial instructions on which way to advance into the city. Guan and the general Hun Jian suggested having the aid force march over Qianling — the hill containing the tomb of Emperor Dezong's ancestor Emperor Gaozong — so that they would have better tactical position. Lu, arguing that doing so was disrespectful, suggested having the aid force march through a valley, despite Hun's protestations that doing so would expose the aid force to catapult attacks by Qin forces. Emperor Dezong agreed with Lu, and subsequently, the aid force was ambushed and, after suffering heavy losses, was forced to withdraw without ever reaching Fengtian. This incident drew a comment from the Song Dynasty/Yuan Dynasty historian Hu Sanxing (the commentator of the Zizhi Tongjian): Soon, Fengtian was in a desperate state, but was saved when Li Huaiguang the military governor of Shuofang Circuit (朔方, headquartered in modern Yinchuan, Ningxia), who had been fighting Tian Yue in the east, arrived in haste and forced Zhu to withdraw back to Chang'an. Meanwhile, though, it had become common knowledge that Li Huaiguang despised Lu, Bai, and Zhao Zan (趙贊) — and that he would recommend to Emperor Dezong that those officials be removed. When Lu heard this, he believed that he had to prevent a meeting between Emperor Dezong and Li Huaiguang at all costs, and therefore suggested to Emperor Dezong order Li Huaiguang to attack Chang'an at once. Emperor Dezong agreed, and ordered Li Huaiguang to rendezvous with Li Sheng, Li Jianhui, and Yang Huiyuan (楊惠元) to attack Chang'an. Li Huaiguang, angry that he was not even able to meet the emperor, began to resent Emperor Dezong. He stopped his army's movement and submitted petitions accusing Lu and the others of crimes and further accusing them of being responsible for the Jingyuan mutiny. Li Huaiguang's accusations were joined by those from many other officials. Around the new year 784, Emperor Dezong was forced to demote and exile Lu, Bai, and