In fact, the thirteen days of Wang Yanji and Yang Gongji are the same day. It should be based on the thirteen taboos, plus the folk legend of Emperor Yan. Generally speaking, Yan has thirteen sons, and because he became the keeper of hades, he became particularly crazy, often boasting that "thirteen sons can't die in a month." As a result, this word reached the Jade Emperor, who decided to punish Yan. So since February, a son has died every month, 28 days apart; On the thirteenth day of the first month, only the last son was left, which happened to be a 28-day cycle. So the prince was particularly jealous of this day, but he died in the end. Therefore, this day is also a "sacrifice to the prince", offering sacrifices to his thirteen sons. Imagine that one day even the prince of Yan is taboo, and people on the ground avoid it, especially on the thirteenth day of the first month, they can't visit the old, the weak and the sick.
Yang Junsong, the founder of Feng Shui.
There is also a story in folklore "Yang Gongbi" from Yang Jiajiang, which is said to be the memorial day of Yang Jiye; Another way of saying it is that when Yang Jiye leads troops to fight, there are always a few days in a year when he is defeated, so he calls these days "the anniversary of Yang Gong's death".