<em><span lang、"EN-US">P→</span></em><span>┐</span><em><span lang="EN-US">Q</span></em><img src="http://oss.ouchn.cn/ddzx/N601/jiaoyu/lssx/images/2tk.png" alt=""><span lang="EN-US">┐<em>P→</em></span><em><span lang="EN-US">Q</span></em>
<img src、"http://oss.ouchn.cn/ddzx/N601/jiaoyu/lssx/images/xk/5/9-3.jpg" alt="">
<span lang、"EN-US">┐<em>P</em></span><span>∧</span><span lang="EN-US">(<em>P</em></span><span>∨</span><em><span lang="EN-US">Q</span></em><span lang="EN-US">)</span><img style="vertical-align: middle;" src="http://oss.ouchn.cn/ddzx/N601/jiaoyu/lssxx/xkrw/03/003.png" alt=""><em><span lang="EN-US">Q</span></em>
<span lang、"EN-US">┐<em>P</em></span><span>∧</span><span lang="EN-US">┐<em>Q</em></span><img src="http://oss.ouchn.cn/ddzx/N601/jiaoyu/lssx/images/2tk.png" alt=""><span lang="EN-US"><em>P</em></span><span>∨</span><em><span lang="EN-US">Q</span></em>