or Tso chuan
Ancient commentary on the Chunqiu ("Spring and Autumn Annals").
It provides extensive narrative accounts and background materials concerning events covered in the Chunqiu , as well as authentic historical documents and written evidence of the philosophical schools of the time. Finally, it provides a comprehensive account of the principal political, social, and military events of the period. It was once believed to have been written by Zuo, an ancient historian about whom virtually nothing is known, but modern scholarship attributes it to an anonymous author of the period 475–221 BCE.