If it is to your advantage, make a forward move; if not, stay where
you are.
This is repeated from XI. § 17. Here I feel convinced that it is an
interpolation, for it is evident that § 20 ought to follow immediately
on § 18. For 動, the _T‘ung Tien_ and _Yü Lan_ have 用. Capt. Calthrop
invents a sentence which he inserts before this one: “Do not make war
unless victory may be gained thereby.” While he was about it, he might
have credited Sun Tzŭ with something slightly less inane.