裡應外合 [里应－－]

Jyutping leoi5 jing3 ngoi6 hap6
Pinyin lǐ yìng wài hé

Definitions (CC-CEDICT)
  1. to coordinate outside and inside offensives (idiom)
  2. (fig.) to act together
Definitions (Wiktionary)
  1. phrase, idiomatic
    to work from the inside in coordination with elements from the outside