Master GongSun Taoism - Sayings of Taoist Master DanYang - Keep a Pure Mind!

Textbook and Source Material from:
Taoist Meditation: Methods for Cultivating a Healthy Mind and Body - Compiled and Translated by Thomas Cleary
Textbook from Understanding Reality - Written by Chang Po-Tuan, Translated by Thomas Cleary
Textbook from Wen Tzu: Understanding the Mysteries - Further Teachings of Lao Zi, Translated by Thomas Cleary