an class="lineno">   67</span>&#160;    point&amp; operator-=(point <span class="keyword">const</span>&amp; p)</div>
<div class="line"><a name="l00068"></a><span class="lineno">   68</span>&#160;    {</div>
<div class="line"><a name="l00069"></a><span class="lineno">   69</span>&#160;        x -= p.x;</div>
<div class="line"><a name="l00070"></a><span class="lineno">   70</span>&#160;        y -= p.y;</div>
<div class="line"><a name="l00071"></a><span class="lineno">   71</span>&#160;        <span class="ke