>&nbsp;&nbsp; </span></div>
<div style="text-indent: 15.75pt"><span style="font-size: medium">下面用四阶群的例子来说明这个问题。抽象地记群元素为e,a,b,c 只要列出一个乘法表，就可以代表一个群。下面给出推导乘法表的步骤：</span></div>
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