m">&nbsp;</span></div>
<div><span style="font-size: medium">虽然4阶群一定有交换律，但这里再次提醒，这并非一个普遍现象。</span></div>
<div><span style="font-size: medium">&nbsp;</span></div></div></div></div></div><div class="row"><div class="column"><h4 class="ui top attached block header">输入格式</h4><div class="ui bottom attached segment font-content"><div style="position: relative; overflow: hidden;"><div class=content><div style="text-indent: 15.75pt"><span style="fon