Huqianjing 虎鈐經 "The classic of the tiger seal" is a military treatise written during the Northern Song period 北宋 (960-1126) by Xu Dong 許洞 (976-1015), courtesy name Dongfu 洞夫 or Yuanfu 淵夫, from Wujun 吳郡 (today's Suzhou 蘇州, Jiangsu). The book was finished in 1004. It has a length of 20 juan and includes 210 chapters, each of which deals with a distinct topic.
The Huqianjing included the concept that in war three realms played an important part, firstly, the realm of man who planned war and battles, second the earth which provided formidable territory to wage war on, and third the realm of Heaven which is involved into war in the shape of the weather, as well as by the influence of stars and deities. Divination thus plays an certain part in warfare, according to the Huqianjing.
A general must be able to observe the enemy and to use the own troops in a way that the enemy was not able to find out what the own troops were planning to do. In a metaphysical way, Xu Dong explains that a general must always be able to identify chances (ji 吉 "luck") in dangers (xiong 凶 "inauspicious situations") and to see when danger was hidden in apparently advantageous situations. The movements of the troops had to be adapted to such changes in luck. A very important foundation for victory was the supply of sufficient food and excellent weapons, in other words, a functioning logistics system.
Xu Dong lists the most important points in a series of conditions: The precondition of a establishing an army was a content population; the precondition of all tactics was caring for sufficient food; the precondition of deploying an army was to make us of advantageous territory; the precondition for victory was to harmonize the troops; the precondition of successful defence was a sufficient stock of supplies; and the precondition of a strong army was the justified application of reward and punishment. A wise general seized all opportunities (duoshi 奪恃), like weather, geographical obstacles, or the army's mood of fighting. He had to feign cowardice to lure the enemy into attack (xi xu 襲虛). And he had to use the own strengths after a victorious battle to pursue the enemy, to trap him, and to annihilate him. It was not always good, warns Xu Dong, to apply traditional methods, but a general had to be flexible and had to adapt his tactics to the actual conditions.