The "Micang Tongxuan Bianhua Liuyin Dongwei Dunjia Zhenjing" (), written in the early Northern Song period, gives an incantation associated with Jiutian Xuannü. By reciting this incantation and performing the paces of Yu (), invisibility to others was said to be achieved. In the "Baopu Zi" (), written by Ge Hong (b. 283), the paces of Yu are described as elements of the divinatory system of "dunjia" (, translated "Hidden Stem") from which the immediate position in the space-time structure of the six ding could be calculated. The six ding are the spirits who are responsible for the position of the irregular gate (), which respresents a rift in the universe. The irregular gate must be approached by performing the paces of Yu and serves as the entrance to the emptiness of the otherworld in which invisibility to evil influences is achieved.