数学符号里面，我们可以看到有一个星星符号，这种符号也是比较常见的符号，今天我们就一起来认识一下这个数学符号，通过这个星星符号也了解一下数学
1：数学里面的星星符号，可以表示为乘于符号，这也是大家都比较熟悉的符号，例于4*4=16 ，也就是4乘于4等于16
2：数学的星星符号也是用于集合的符号，里面于面的例子
应用在正则表达式
Kleene 星号应用於字符串集合的例子：
{"ab","c"}* = {ε,"ab","c","abab","abc","cab","cc","ababab","ababc","abcab","abcc","cabab","cabc","ccab","ccc",...}
Kleene 星号应用于集合的例子：
{'a','b','c'}* = {ε,"a","b","c","aa","ab","ac","ba","bb","bc",...}
