Because the heavenly stems have ten digits and the earthly branches have twelve digits, in the process of heavenly stems and earthly branches's combination, there will be ten cycles of heavenly stems and there will be no two earthly branches. This is called "emptiness". For example, in Jia, there are only ten numbers from Jiazi to Jiazi, but the double digits of Xu and Hai do not appear. This phenomenon is called "Xunkong".
Xunkong's law is: "Jia Zi has no sorrow for ten days, JOE has no Shen You for ten days, Shen Jia has no noon for ten days, Wu Jia has no Tatsumi for ten days, Chen Jia has no pubic hair for ten days, and Jia Yin has no ugliness for ten days."
Xun Kong has no fixed good or bad luck. When running, evil things enter the sky and are auspicious; And when something auspicious reaches the sky, it is a loss of face.