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<div><span class="kw">theorem </span><a NAME="T13"><span class="comment"><font color="firebrick">:: TREES_2:13</font></span><br/></a><div class="add"> for <font color="Olive" title="b1">W</font> being   <a href="trees_1.html#NM1" title="TREES_1:NM.1">Tree</a><br/>  for <font color="Olive" title="b2">w</font> being    <a href="trees_1.html#M1" title="TREES_1:mode.1">Element</a> of <font color="Olive" title="b1">W</font>  st <font color="Olive" title="b2">w</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a>  <a href="xboole_0.html#K1" title="XBOOLE_0:func.1">{}</a>  holds <br/><font color="Olive" title="b1">W</font> <a href="trees_2.html#K2" title="TREES_2:func.2">-level</a> 1 <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a>  <a href="trees_2.html#K1" title="TREES_2:func.1">succ</a> <font color="Olive" title="b2">w</font></div></div>
