 In its most widespread codification, which originates in the Southern Lineage, the Neidan practice consists of three main stages (Despeux 1979: 55–82; Robinet 1995: 147–64; Wang Mu 2011). Its purpose is to lead an adept from the postcelestial to the precelestial domains through the gradual reintegration of each of the three main components of the human being—Essence, Breath, and Spirit—into the one that precedes it, culminating in the reversion to the state of Non-Being (wu), or Emptiness (xu, kong). While this is the function of alchemy per se, certain authors indicate that the process of ascent to the precelestial domain should be followed by a new descent or return to the postcelestial domain, in order to merge them with one another.