《汉书·传·窦田灌韩传》
当时单于进入长城武州塞，距离马邑尚有一百多里，发觉其中有诈，因此引兵撤回。
于是单于入塞，未至马邑百余里，觉之，还去。
At that time, the Chanyu entered Wuzhou Pass of the Great Wall, which was still over a hundred li away from Mayi; he realized that there was a trick, so he withdrew his troops.
<s>[INST] Kindly elucidate the central themes in this passage in English: 于是单于入塞，未至马邑百余里，觉之，还去。 [/INST] At that time, the Chanyu entered Wuzhou Pass of the Great Wall, which was still over a hundred li away from Mayi; he realized that there was a trick, so he withdrew his troops.</s>
Kindly elucidate the central themes in this passage in English: 于是单于入塞，未至马邑百余里，觉之，还去。
user
At that time, the Chanyu entered Wuzhou Pass of the Great Wall, which was still over a hundred li away from Mayi; he realized that there was a trick, so he withdrew his troops.
assistant