《战国策·齐二·秦攻赵长平》
秦王分析说： 如今齐、楚来救援赵国，如果他们联合作战，寡人就退兵；如果他们一盘散沙，我就趁机攻打它。 
秦计曰： 齐、楚救赵，亲，则将退兵；不亲，则且遂攻之。 
The King of Qin analyzed and said: Qi and Chu have come to aid Zhao; if they fight together, then I shall withdraw. If they do not work together, then I shall seize the opportunity to attack them.