Chapter 6 of Tao Te Ching: "The immortal god in the valley is called Xuanzang. The gate of Xuanzang is the root of heaven and earth. If it exists, it will be continuous, and if it is not used, it will be diligent. "
Specifically, it refers to the theory that heaven and earth, mouth and nose, up and down, father, essence, mother, blood and kidney, Shen Yuan, Huang Ting's abdomen and heart are left and right orifices.
Some people think that the entrance is a mystery. In Wuzhen Zhi Zhi, "The movement of the Valley God is also the door of Xuanzang. This door is the four parts of the human body. In the middle of heaven and earth, it hung a hole in vain Sometimes it opens and closes, and the action is natural. It's called the porch, also called the wonderful gate. " See the article "Know something about the entrance". Xuanzang, desire also. Desire triggers thinking.