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In the Book of Changes, "seven" is a changing number and a resurrected number. I ching: "repeat the same thing and come back in seven days. It will be fine." Seventh, yang number and days. After the sun between heaven and earth is extinguished, it can be resurrected after seven days. This is the way of heaven and earth, the principle of yin-yang cycle. "Seven" also has mysterious colors, such as the seven stars in the sky, the seven emotions on earth, the seven colors of color, the seven tones of music, the seven rhymes of poetry and the seven senses of human body. "Seven" is also a human life cycle, starting from the age of seven and entering adolescence at the age of fourteen.