What is the art of yin and yang?

Yin and Yang Army is one of the four schools of military strategists. There is a classic description of the so-called Yin-Yang soldiers in the History of Art and Literature of Han Dynasty: "Yin-Yang people, those who are in time, push punishment and morality, fight with each other, and because of five victories, fake ghosts and gods think of them as helpers." Choosing the right time, using punishment, using soldiers and winning five victories show that the soldiers' yin and yang family is actually the application or extension of various forms of martial arts in military theory and practice under the framework of yin and yang and five elements. The "fake ghost gang" refers to all the military applications of magic and witchcraft with the help of ghosts and gods, and can also be included in the categories of soldiers and yin and yang. Bing Yinyang's family not only includes all kinds of military skills in the past dynasties, such as divination, astrology, divination, dreaming, sacrifice, prayer, cursing, aversion to victory, various occupations, witchcraft and so on. And it is also different from the previous military skills. Its appearance marks that the history of China's military skills has entered a new stage.