《资治通鉴·宋纪·宋纪十一》
孝武帝命令对历法有研究的人同祖冲之辩论，但驳不倒祖冲之。
上令善历者难之，不能屈。
Emperor Xiaowu ordered people who studied the calendar system to debate with Zu Chongzhi, but they failed to refute him.
<s>[INST] Kindly elucidate the central themes in this passage in English: 上令善历者难之，不能屈。 [/INST] Emperor Xiaowu ordered people who studied the calendar system to debate with Zu Chongzhi, but they failed to refute him.</s>
Kindly elucidate the central themes in this passage in English: 上令善历者难之，不能屈。
user
Emperor Xiaowu ordered people who studied the calendar system to debate with Zu Chongzhi, but they failed to refute him.
assistant