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As soon as the whole army had passed by, the hidden troops fell

on his rear, while Ts'ao himself turned and met his pursuers in

front, so that they were thrown into confusion and annihilated.

Ts'ao Ts'ao said afterwards: "The brigands tried to check my army

in its retreat and brought me to battle in a desperate position:

hence I knew how to overcome them."]

36. When you surround an army, leave an outlet free.

[This does not mean that the enemy is to be allowed to escape.

The object, as Tu Mu puts it, is "to make him believe that there

is a road to safety, and thus prevent his fighting with the

courage of despair." Tu Mu adds pleasantly: "After that, you may

crush him."]

Do not press a desperate foe too hard.