Zhèng Yǐn 鄭隱 was a Five-Dynasties Daoist author, traditional attributed author of KR5c0324 Zhēn yuán miào dào yào lüè 真元妙道要略 — a Daoist alchemical summary, often cited as containing the earliest mention of an early form of gunpowder (huǒ yào 火藥) in connection with saltpetre/sulfur alchemical mishaps. (Distinguish from the Eastern-Jìn Zhèng Yǐn 鄭隱, teacher of 葛洪 — different person.)