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<div><span class="kw">theorem </span><span class="lab"><font color="Green" title="E13">Th14</font></span>: <a NAME="T15"><span class="comment"><font color="firebrick">:: TREES_1:15</font></span><br/></a><div class="add"> <a href="trees_1.html#K1" title="TREES_1:func.1">ProperPrefixes</a> <a href="xboole_0.html#K1" title="XBOOLE_0:func.1">{}</a> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a>  <a href="xboole_0.html#K1" title="XBOOLE_0:func.1">{}</a> </div></div>
