What Is Symmetry?
Everyone has some idea of what symmetry is. We recognize the bilateral symmetry of the human body, of the bodies of many other animals, and of numerous objects in our environment. We consider a scalene triangle to be completely lacking in symmetry, while we see symmetry in an isosceles triangle and even more symmetry in an equilateral triangle. That is only for starters. Any reader of this book can easily point out many more kinds and examples of symmetry. For an elementary introduction to symmetry see my book [S22], and for a more advanced introduction, see Weyl [S31]. Escher has given us fantastic illustrations of geometric (and color) symmetry, to be enjoyed in [M16, M17, M40, and M55]. And see also [S13, S30, M25, and M35].
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