There are many styles of calligraphy, including implicit, simple, bold, bold, aesthetic and naive. People often say that "Yan Gu" is an evaluation of the different calligraphy styles of famous calligraphers Yan Zhenqing and Liu Gongquan in the Tang Dynasty. The former is rough and bold, vigorous and has the beauty of neatness and generosity; The latter has compact structure, strong bones and strong aesthetic feeling.