To the west, the argument is as follows:
Sima Qian [Historical Records/Lao Tzu's Biography of Han Fei] records that Lao Dan wrote five thousand words [Tao Te Ching] for Guan Ling Yin Xi, and when he arrived at Hangu Pass in the west, he never knew his final destination.
Why do you come from the East? The argument is as follows:
Purple air comes from the east, which is an auspicious omen.
Interpretation: According to legend, before Laozi crossed Hangu Pass, Guan Yinxi saw the purple gas coming from the east and knew that there were saints to pass. Sure enough, I came riding a green cow. A metaphor for good luck.
Out: The Story of the Immortal: "I traveled to the Western Heaven, and I saw the purple floating in the shade, and I passed the green cow."