What are Yin and Yang, how do Yin and Yang relate to us, and is the end result of neidan something that is pure Yang, or still related to Yin and Yang somehow? 
  I see Yin and Yang as emblematic of the two side channels that interact at each dantian, so to me entirely relevant on a personal level throughout the inner journey, and the end result, ie., alchemical gold, as a contribution from both channels, to be placed in the central channel beyond yin and yang. 
  “The trigrams of the Book of Changes are used to show how the alchemical process consists of extracting the precosmic Real Yin (zhenyin) and Real Yang (zhenyang) from Yang and Yin as they appear in the cosmos, respectively, and in combining them to produce an elixir that represents their unity.”  Here
  (Anything that seems to suggest only pure Yang as an end point seems tarred by patriarchal conditioning to me.)