The Ruler of Wei gave the order； and he sent the mand by the hand of Minister Han Ji and gave him authority to warn Cao Zhen against giving battle。
Sima Yi escorted the royal messenger out of the city and； at parting； said； 〃I am giving this magnificent opportunity to obtain glory to Cao Zhen； but do not tell him the suggestion was mine； only quote the royal mand。 Tell him that defense is the best； pursuit is to be most cautious； and he is not to send any impetuous leader to follow up the enemy。〃
Han Ji agreed and took leave。
Cao Zhen was deep in affairs connected with his army when they brought news of a royal messenger； but he went forth to bid Han Ji wele。 When the ceremonial receipt of the edict had e to an end； he retired to discuss matters with Guo Huai and Sun Li。
〃That is Sima Yi's idea；〃 said Guo Huai with a laugh。
〃But what of the idea？〃 asked Cao Zhen。
〃It means that he perfectly understands Zhuge Liang's plans； and he will eventually have to be called in to defeat Shu。〃
〃But if the Shu army holds its ground？〃
〃We will send Wang Shuang to reconnoiter and keep on the move along the by…roads so that they dare not attempt to bring up supplies。 They must retreat when they have no more to eat； and we shall be able to beat them。〃
Then said Sun Li； 〃Let me go out to Qishan as if to escort a convoy from the West Valley Land； only the carts shall be laden with bustibles instead of grain。 We will sprinkle sulfur and saltpeter over wood and reeds。 The troops of Shu； who lack supplies； will surely seize the convoy and take it to their own camp； when we will set fire to the carts。 When they are blazing； our hidden men can attack。〃
〃It seems an excellent plan；〃 said Cao Zhen。
And he issued the re