The Essence of the Book of Changes from the Three Heavens

The 1-volume Essence of the Book of Changes from the Three Heavens ( 《三天易髓》 San Tian Yisui ) was written by Yingchanzi Li Zhichun and edited by Hunranzi. It contains four parts: 三天易髓
 * 1) Supreme Ultimate in Confucian Terms ( 儒曰太極 Ru Yue Taiji ) • The Direct Pointing to Fire Phases ( 火符直指 Huofu Zhizhi ). This part explains inner alchemy using the theory of Book of Changes in fifteen poems and notes about "not using the hidden dragon" in the Book of Changes to correspond to the number of 3 multiplies 5. It says: The so-called pearl of mystery ( 玄珠 Xuanzhu ) of Buddhism, Supreme Ultimate of Confucianism and Golden Elixir ( 金丹 Jindan ) are just three names for the same thing.
 * 2) Chart Illustrating Golden Elixir Clearly ( 金丹了然圖 Jindan Liaoran Tu ). The chart is lost while nine 8-lined poems of 5 words per line remain, which are about the practice of inner alchemy: beginning, setting furnace ( 安爐 Anlu ), fetching medicine ( 采藥 Caiyao ), running breath, keeping full, nourishing elixir, harmonizing spirit ( 調神 Tiaoshen ), leaving embryo ( 脫胎 Tuotai ), completion.
 * 3) Complete Enlightenment ( 圓覺 Yuanjue ) in Buddhism and Direct Pointing to Heart Sutra ( 心經直指 Xinjing Zhizhi ). This part explains the Buddhist Heart Sutra, holding that the sutra focuses on emptiness from beginning to end. It explains Buddhism with Daoist thoughts.
 * 4) Commentary of the Book of Secret Correspondence. This part explains the Book of Secret Correspondence as exposing the correspondence of Yin and Yang and way of all things. The part is meant to prove Daoism with Confucianism and Buddhism, and thus tell the learners that the three teachings are just the same. Collected in Subsection of Skills, Pervasive Perfection Section ( 洞真部 Dongzhen Bu ) of the Daoist Canon of the Zhengtong Era, the book is important for the study of Daoist syncretism and inner alchemy.