Instead , Tan suggested , Weibo should enter into a secret agreement with Chengde .
Weibo would launch a false attack on Chengde and capture a county to outwardly show Emperor Xianzong that he was not rebelling against imperial authority .
Instead , Tan suggested , Weibo should enter into a secret agreement with Chengde whereas Weibo would launch a false attack on Chengde and capture a county to outwardly show Emperor Xianzong that he was not rebelling against imperial authority .