Yan refers to Yan Zhenqing, who is called "Yan Jin" because of his plump calligraphy, and Liu refers to Liu Gongquan, whose vigorous calligraphy is called "Liu Gu".
The idiom comes from Song Fan Zhongyan's "Essay on the Stone Sacrifice for Bachelor": "The pen of the pen is Yan Gu.
Idioms are used as objects and attributes; Calligraphy.
The example given is heartbroken poetry, which can be regarded as the history of speech, speech, care, dedication and righteousness.
★ Yuan Guan Hanqing's "Pu Tian Le Zhi Xi De Shu" Song Luyou's "Tang Xia Xue Que" poem: "I think this painting is like a strange book, and Yan pursues Ou Yu." "Surprise at the Second Moment" Volume 2: "This book is full of bones and muscles, and there is nothing illegal.