Xun Yu said, "O Leader, you are brave, but we must consider the present circumstance. We cannot start a sudden war just as the capital has changed. However, there is a certain ruse known as 'Rival Tigers and One Prey'. Liu Bei has no decree authorizing him to govern the region. You, Sir Prime Minister, can procure one for him, and when sending it, and so conferring upon him the right in addition to his might, you can enclose a private note telling him to get rid of Lu Bu. If he does, then he will have lost a vigorous warrior from his side, and he could be dealt with as occasions serve. Should he fail, then Lu Bu will slay him. This is the 'Rival Tigers and One Prey' ruse: They wrangle and bite each other."
Luo Guanzhong, Romance of the Three Kingdoms (trans. C.H. Brewitt-Taylor)