The rhyme group 侵尋 "qīn"-"xún" (-im, -əm) of the "Zhongyuan Yinyun" 中原音韵/中原音韻, an Old Mandarin pronunciation guide written by Zhou Deqing (周德清) in 1324. The rhyme group is subdivided by tone (reading from right to left): level tone (平聲 "píngshēng") split into 陰 "yīn" and 陽 "yáng", rising tone (上聲 "shǎngshēng") and departing tone (去聲 "qùshēng"). Words within each tone are placed in homophone groups.