What are the three calligraphy techniques edited by Cao Jinhong?

Calligraphy Techniques edited by Cao Jinhong are Calligraphy Techniques, Complete Works of Calligraphy and Hard Pen Calligraphy. Handed down Calligraphy Techniques includes three volumes: Calligraphy Techniques, Complete Works of Calligraphy and Hard Pen Calligraphy, which contains the inscriptions and seals of famous calligraphers from ancient times to the present, such as Qin Lisi, Tang Liyang Bing, Yuan Zhao Mengfu, Wu Qinxi Zi and modern Wu Changshuo. It is a rare calligraphy book for the majority of calligraphy lovers to find, study and ponder famous works.