Mathematical Physics: Classical Mechanics
《Mathematical Physics: Classical Mechanics》 · 第 8 页 · Chapter 1，pretzel knots and links 段落及 Figure 1.7（任意束数）
An example, which later will be featured often, is that of pretzel knots and links. The pretzel link \(P(a_1,a_2,\ldots,a_n)\) is shown in Figure 1.7. Here the \(a_i\) are integers indicating the number of crossings in the various “tassels” of the diagram. If \(a_i\) is positive, the crossings are in the sense shown (the complete “tassel” has a right-hand twist); if \(a_i\) is negative, the crossings are in the opposite sense. As \(n\) varies and different values are chosen for the \(a_i\), this gives an infinite collection of links.