Secret and Unique Mind Method (1-2)

This book is very rare. It contains the summary and annotation of predecessors' experience, including the mystery and the breaking of the underground branch. Now all the books on the market are the remnants of mysterious secrets, full of the essence of ancient Chinese without underground branches and annotations. Just like gobbledygook, it's a collector's edition. There is still a lot of content that I can't understand. It would be nice to have a companion in this way, haha.