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I have never been proficient in medicine. I once followed a few close friends and their descendants, engaging in discussion and mutual refinement, and roughly grasped the general principles. I then realized that this path is connected to the *Yijing* (Book of Changes); it is both the most subtle and the most simple. In recent times, practitioners of medicine have failed to thoroughly understand its origins and lineage. They favor bizarre and eccentric theories to deceive people, and their vague and fragmented explanations have caused significant harm. A clansman, Deng Linzi, devoted his heart to this discipline, extensively synthesizing and deeply contemplating. For decades, he lived quietly amidst the water and bamboo of the eastern city, achieving great fame without seeking recognition. After the Shen and You years, literati and scholars put aside their brushes and inkstones, abandoned the imperial examinations, and carried their book boxes to study at Deng Linzi's door. Initially, Deng Linzi helped them uncover the profound mysteries of Yin-Yang and generation/transformation in the *Suwen* (Basic Questions), and clarify the subtleties of meridians and acupoints in the *Lingshu* (Spiritual Pivot). Subsequently, he analyzed the difficulties in the *Nanjing* (Classic of Difficult Issues), explored the diagnostic cases of Cang Gong, expounded upon Zhang Zhongjing, discussed Wang Shuhe, and examined the similarities and differences among various schools such as He Jian, Jie Gu, Dong Yuan, and Dan Xi. In all these areas, he investigated the roots and reached a balanced conclusion. Dozens of students under his guidance were prominent figures of the time, and one could worry that none would fail to open their minds and broaden their horizons. Finally, he selected the *Siyan Juyao* (Four-Character Essentials) compiled by Zixu Zhenren and provided annotated interpretations. From pulse diagnosis, he proceeded to syndromes; from syndromes, he proceeded to formulas. He integrated the essentials of the *Lingshu*, *Suwen*, and other schools previously expounded into content that was plain, practical, and accessible, allowing readers to see clearly as if pointing at their palm. This is what is meant by "the most subtle, the most simple." Treating common things as common, and precious things as precious. How do those偏僻 (remote/narrow-minded) and absurd theories that deceive and mislead people compare? Upon completion, the book was renamed *Yideng Xuyan* (Continuation of the Medical Lamp Flame). Through this continuation, the light can illuminate all directions. Its merit for future generations is immeasurable. Deng Linzi's aspirations were serene and detached, showing no interest in pursuing fame and profit. After clinical consultations, he would close his door and lower his curtains, drinking and reciting poetry to find joy in himself. His lofty demeanor was thus. My friend Zhang Qingzi was profound and tranquil, deeply mastering the principles of the *Yijing*. He lived across the water from Deng Linzi. The disciples of both families had no distinctions between them; they asked questions and debated with harmony, mutually benefiting and enhancing each other. This was widely transmitted as a grand event in the literary and medical circles, and I was also able to visit several times to listen to his profound discussions. Alas! Someone like Deng Linzi has advanced to the level of the Dao; how can he be described merely as possessing skill? In early summer of the Renchen year, the junior clan member Qi respectfully wrote the preface.