To be equally matched; to be on a par with each other.
分不出高低好坏。形容水平相当。
唐·陆龟蒙《蠹化》翳叶仰啮，如饥蚕之速，不相上下。”
The two chess players are so evenly matched that their games are always neck-and-neck.
Learn the next connected idiom: 不相上下 (bù xiāng shàng xià) → 下落不明 (xià luò bù míng)
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