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<div><span class="kw">theorem </span><a NAME="T9"><span class="comment"><font color="firebrick">:: INTERVA1:9</font></span><br/></a><div class="add"> for <font color="Olive" title="b1">U</font> being   non  <a href="xboole_0.html#V1" title="XBOOLE_0:attr.1">empty</a>   <a href="hidden.html#M2" title="HIDDEN:mode.2">set</a>  holds   <a href="xboole_0.html#K1" title="XBOOLE_0:func.1">{}</a>  is    <a href="interva1.html#M1" title="INTERVA1:mode.1">IntervalSet</a> of <font color="Olive" title="b1">U</font></div></div>
