[wài hé lǐ yìng]   

外    合    里    应    外面攻打，里面接应。

里应外合，汉语成语，指的是外面攻打，里面接应。出自元·杨梓《博让理德》

Act from inside in coordination with attack from outside

外厉内荏    外方内员    外温内厚    外圆内方    外巧内嫉