[Tu Yu gives the best exposition of the meaning: "We ostentatiously do things calculated to deceive our own spies, who must be led to believe that they have been unwittingly disclosed. Then, when these spies are captured in the enemy’s lines, they will make an entirely false report, and the enemy will take measures accordingly, only to find that we do something quite different. The spies will thereupon be put to death." As an example of doomed spies, Ho Shih mentions the prisoners released by Pan Ch’ao in his campaign against Yarkand. (See p. 132.) He also refers to T’ang Chien, who in 630 A.D. was sent by T’ai Tsung to lull the Turkish Kahn Chieh-li into fancied security, until Li Ching was able to deliver a crushing blow against him. Chang Yu says that the Turks revenged themselves by killing T’ang Chien, but this is a mistake, for we read in both the old and the New T’ang History (ch. 58, fol. 2 and ch. 89, fol. 8 respectively) that he escaped and lived on until 656. Li I-chi played a somewhat similar part in 203 B.C., when sent by the King of Han to open peaceful negotiations with Ch’i. He has certainly more claim to be described a "doomed spy", for the king of Ch’i, being subsequently attacked without warning by Han Hsin, and infuriated by what he considered the treachery of Li I-chi, ordered the unfortunate envoy to be boiled alive.] 13. _Surviving spies_, finally, are those who bring back news from the enemy’s camp. [This is the ordinary class of spies, properly so called, forming a regular part of the army. Tu Mu says: "Your surviving spy must be a man of keen intellect, though in outward appearance a fool; of shabby exterior, but with a will of iron. He must be active, robust, endowed with physical strength and courage; thoroughly accustomed to all sorts of dirty work, able to endure hunger and cold, and to put up with shame and ignominy." Ho Shih tells the following story of Ta’hsi Wu of the Sui dynasty: "When he was governor of Eastern Ch’in, Shen-wu of Ch’i made a hostile movement upon Sha-yuan. The Emperor T’ai Tsu [? Kao Tsu] sent Ta-hsi Wu to spy upon the enemy. He was accompanied by two other men. All three were on horseback and wore the enemy’s uniform. When it was dark, they dismounted a few hundred feet away from the enemy’s camp and stealthily crept up to listen, until they succeeded in catching the passwords used in the army. Then they got on their horses again and boldly passed through the camp under the guise of night-watchmen; and more than once, happening to come across a soldier who was committing some breach of discipline, they actually stopped to give the culprit a sound cudgeling! Thus they managed to return with the fullest possible information about the enemy’s dispositions, and received warm commendation from the Emperor, who in consequence of their report was able to inflict a severe defeat on his adversary."]