permutations

置换

Multiplication of permutations, unlike multiplication of numbers, is not always commutative. 置换的乘法不同于数的乘法，它并不一定满足交换律。

It turns out that all these problems can be solved at once, provided we learn enough about the cycle structure of permutations. 结果是，所有这些问题都可以一次解决，只要我们充分地了解各置换的循环结构。