For example, flowers and butterflies are undoubtedly beautiful, but careful observation shows that the formation of flowers and butterflies' wings has strict modeling rules: their patterns and lines are symmetrical and very harmonious, and their colors are very soft, and their geometric modeling accuracy often surprises mathematicians. Others, such as the crystallization of ice and snow, the bending of rainbow, the vein of leaves, the hexagonal structure of honeycomb, and even the limbs of human body, all have accurate geometric modeling rules. Modern physicists have found that the operation of celestial bodies, the structure of atoms and even many mathematical and physical formulas are very harmonious, orderly and concise. No wonder the German astronomer Kepler said, "Mathematics is the prototype of the beauty of this world." All these formal laws are not created by human beings according to their own wishes, but by ingenious nature, but they are beautiful. Therefore, the variability and unity of the Book of Changes, that is, "circulation" and "harmony" are both laws of nature and beauty.