xuanguan yiqiao 玄關一竅
one opening of the mysterious barrier
※ This term is equivalent to One Opening (yiqiao), Mysterious Barrier (xuanguan), and Mysterious Opening (xuanqiao).
① The Center.
⊛ This Opening is not a common opening: it is formed by the joining of Qian ☰ and Kun ☷. It is called Cavity of Spirit and Breath, and within there are the essences of Kan ☵ and Li ☲. 此竅非凡竅，乾坤共合成，名為神氣穴，內有坎離精。 (Four Hundred Words on the Golden Elixir, poem 7, trans. in Taoist Internal Alchemy: An Anthology of Neidan Texts, p. 95)
⊛ The One Opening of the Mysterious Barrier is the palace of the four cardinal points. 玄關一竅，四正宮也。(*) (Xiao Tingzhi, Questions and Answers on the Golden Elixir, trans. in Taoist Internal Alchemy: An Anthology of Neidan Texts, p. 149)
(*) According to this definition, the four cardinal points reside together in the One Opening.
⊛ The One Opening of the Mysterious Barrier has no extension and no position, no form and no image. 玄關一竅，無方無所，無形無象。 (Awakening to Reality, "West River Moon", Comm. Liu Yiming)
② The residence of Spirit, Breath, and Essence, joined to one another.
⊛ The One Opening of the Mysterious Barrier is the cavity of Spirit, Breath, and Essence. 玄關一竅乃神氣精之穴也。 (Xiao Tingzhi, Questions and Answers on the Golden Elixir, trans. in Taoist Internal Alchemy: An Anthology of Neidan Texts, p. 147)
③ The symbolic location where the entire alchemical work occurs.
⊛ In the wondrous operation of compounding the Elixir, it is essential to understand the One Opening of the Mysterious Barrier. 作丹妙用，要明玄關一竅。 (Wang Jie, comm. to Mirror for Compounding the Medicine, poem 12)
⊛ This is the opening that generates Heaven, Earth, and humans; this is the hometown of Saints, Buddhas, and Immortals. You arrange the furnace and set up the tripod here; you collect the Medicine and refine it here; you coagulate the Elixir here; and you deliver it here. Being is here, Non-Being is here. The beginning and the end of all operation are here. 乃生天生地生人之孔竅，成聖成佛成仙之家鄉。安爐立鼎在此，採藥烹煉在此，結丹在此，脫丹在此，有為在此，無為在此，始終功用總在此。 (Liu Yiming, Cultivating the Tao, chap. 16)