辅车唇齿

Explanation: Auxiliary: mouth next to the cheek bone. Car: gums, bone is gums. Cheek bone and gum bone, lips and teeth. Refers to the interdependence of the two sides. 　　Source: Phrase from the "five-year public Zuo Xi," saying the so-called 'auxiliary car dependent, interdependent', its Yu Guo that also. "The so-called 'auxiliary car dependent, interdependent', its Yu Guo that also." 　　Examples: Elegy of the "Word of Oracle," and this naturally ~. ★ Guo, "Study of Ancient China" third chapter