Who are the four great calligraphers of the Northern Song Dynasty in Water Margin?

Su Shi, Huang Tingjian, Mi Fei, Cai Jing. According to the novel Water Margin, Su Shi, Huang Tingjian, Mi Fei and Cai Jing were four great calligraphers in the Northern Song Dynasty. The Water Margin is a novel written by Shi Naian at the end of Yuan Dynasty and the beginning of Ming Dynasty (most of the existing publications are signed by Shi Naian and Luo Guanzhong).