This Chinese of Nearly Equal--Bu Xiang Shang Xia is 不相上下, and Pin Yin bù xiāng shàng xià.
Lu Gui Meng (陆龟蒙) was a famous poet and writer at the end of Tang
Dynasty. One of his most well-known articles was "Du Hua" (meaning the
caterpillar turned into a butterfly), in which Lu Gui Meng satirized
those hypocrites who assumed solemn airs in public but coveted after
fame and gains in private.
The idiom of "Nearly Equal--Bu Xiang Shang Xia" comes from a sentence of
this article, which reads " 翳叶仰啮，如饥蚕之速，不相上下" meaning the caterpillar
hiding underneath a leaf was eating the leaf as fast as a silkworm
chewing mulberry leaves.Later, people derived the idiom of "Nearly Equal--Bu Xiang Shang Xia
(不相上下)" from this article. Its meaning is the same as the English phrase
"Horse and Horse".