1 Introductio n
Take a piece of string. Tie a knot in it. Now glue the two ends of the string
together t o form a knotted loop . The result is a string that has no loose
ends and that is truly knotted. Unless we use scissors, there is no way that
we can untangle this string. (See Figure 1.1.)
Figure 11 Formin g a knot from a piece of string.