https://www.amazon.com/dp/0985958855/ref=tsm_1_fb_lk
This book is fantastic in Chinese; the preview on Amazon suggests that something of the original prose's art was lost in translation, but as a resource for anybody who would like to learn more about the way in which Chan is a child of Laozi and Zhuangzi's Daoism--as well as glimpse some of the ways in which Chan, centuries later, helped give birth to Complete Reality Daoism--I suspect that it may well be the best book out there. The author liberally quotes from primary sources, provides clear explanations of obscure Tang and Song Dynasty-era Chan teachings, and gives many examples where Chan teachers expanded upon Laozi and Zhuangzi's original teachings. Given how closely these two traditions are intertwined, it is difficult to find sources that pick them apart and place the historical and philosophical threads in a clear light like Professor Wu does. I think that cultivators, scholars, and the curious will all find Wu's book extremely useful.
For those who read Chinese, the original is called ãįĶŠčččã, and the author is åģæĄ.