In the Middle Ages, every vowel with the same rhyme must meet two conditions: (1) the same or similar abdominal sound and the same ending; Similarities and differences between rhymes, whether they exist. (2) The tone is the same. If the tone is different, even if the vowel structure is the same, it is considered as different rhyme. For example, the rhyme "Geng" in Guang Yun contains four vowels: [a? の、ぃia？ の、ぃua？ の、iua？ ], these four vowels are the same after the rhyme. Please look at the rhyming reality in the Tang Dynasty: I feel sorry for the quiet grass stream [A? 〕,? There is an oriole singing in the tree [ia? 〕。 ? The rain brought by the spring tide comes late and comes quickly. Cross the wild unmanned boat [ua? ☆ Wei Shi's Xixi Chuzhou has three rhymes: sound, brightness and constancy. Although the sound has no rhyme, Ming and Heng have rhyme and are different from each other, because its rhyme, ending and tone are the same (middle ancient sounds are flat), so it can be bet.