The vowel is close, the vowel is the same but not belongs to Duizhuan, rhyme tail is the same and the vowel is close, they are Heyun.
凡元音相近，或元音相同而不属于对转，或韵尾相同且元音相近，叫做合韵。
2
The gesture for this, the vowel most far forward in the mouth, is made by bringing the arms close together and parallel to one another, as if in making a tube.