《北齐书·列传·卷四十二》
敌人如果闭关不出。可以攻取黄河以束的地区，长安就会陷入困顿，自然就困死了。
彼若闭关不出，则取其黄河以东，长安穷蹙，自然困死。
If the enemy chooses to hole up, we can capture the regions east of the Yellow River, so Chang’an will be besieged and naturally perish.
<s>[INST] Identify the key themes in this Classical Chinese text and explain them in English: 彼若闭关不出，则取其黄河以东，长安穷蹙，自然困死。 [/INST] If the enemy chooses to hole up, we can capture the regions east of the Yellow River, so Chang’an will be besieged and naturally perish.</s>
Identify the key themes in this Classical Chinese text and explain them in English: 彼若闭关不出，则取其黄河以东，长安穷蹙，自然困死。
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If the enemy chooses to hole up, we can capture the regions east of the Yellow River, so Chang’an will be besieged and naturally perish.
assistant