《六韬·龙韬·阴书》
武王问太公说： 率领军队深入敌国境内，国君与主将想要集结兵力，根据敌情进行灵活的机动，出其不意的战胜敌军。然而情况复杂，用阴符难以说明问题，彼此相距又十分遥远，言语难通。在这种情况下应该怎么办？ 
武王问太公曰： 引兵深入诸侯之地，主将欲合兵行无穷之变，图不测之利，其事繁多，符不能明，相去辽远，言语不通，为之奈何？ 
King Wu asked Taigong: When commanding troops deep into enemy territory, the monarch and the general want to assemble their forces and adapt to the enemy situation in order to win by surprise. However, the situation is complex and it is difficult to explain things with secret symbols. Furthermore, the distance is great and words are difficult to communicate across. What should be done in such a situation?