《资治通鉴·汉纪·汉纪六十》
算来曹仁部被围未超过十天，还可以坚守，然后里外一齐发动，一定可以打败关羽。
计北军不过十日，尚足坚守，然后表里俱发，破贼必矣。
In all likelihood, Cao Ren's troops have been under siege for less than ten days and can still hold out. Then we can launch an attack from inside and outside and are bound to defeat Guan Yu.