"Yan" refers to Yan Zhenqing and "Liu" refers to Liu Gongquan. They are all four famous regular script writers in the ancient calligraphy history of China: Yan Zhenqing's calligraphy is clumsy and appears healthy and free and easy. Liu Gongquan's calligraphy has sharp edges and corners, and is famous for strengthening bones. "Yan Gu" means that their style is as strong as bones and muscles. Yan Liujin is from Song Fan Zhongyan's Bachelor of Sacrificing Stones: "Man Qing's pen, Yan Liujin." Yan Liu's and Yan Liu's calligraphy are both powerful, but their styles are different. Also known as excellent calligraphy.