Name for a compendium of twenty-one essays on the Taoist knowledge that a ruler needs. It describes the universe as a harmonious unity, which the ruler must cultivate himself to understand. It is a hard-headed, practical work that stands opposed to the forms and rites of Confucianism, and opposed as well to the more superstitious developments of Taoism aimed at immortality. As a result its principal author, Liu An was eventually executed.