example
        is given by the <a href="http://en.wikipedia.org/wiki/Natural_number" target="_top">natural
        numbers</a> where the operator arithmetic obeys the following rules (using
        the standard notation for <a href="http://en.wikipedia.org/wiki/Number" target="_top">number
        systems</a>):
      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            <span class="inlinemediaobject"><img src="../../../libs/units/images/