p">[</span>,<span class="fl">3</span><span class="op">]</span> <span class="op">&lt;-</span> <span class="va">X</span><span class="op">[</span>,<span class="fl">3</span><span class="op">]</span> <span class="op">-</span> <span class="fu"><a href="../reference/Proj.html">Proj</a></span><span class="op">(</span><span class="va">X</span><span class="op">[</span>,<span class="fl">3</span><span class="op">]</span>, <span class="va">Z</span><span class="op">[</span>,<span class="fl">1</span><span class="op">]</sp