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<b>let </b><font color="Maroon">D</font> be  non <a href="xboole_0.html#V1">empty</a>  <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">T</font> be   <a href="trees_2.html#NM6">DecoratedTree</a> of <font color="Maroon">D</font>;<br/>



<a NAME="E1:25"/>
 <a href="relat_1.html#K2">rng</a> <font color="Maroon">T</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">D</font>
 
<b>by </b><i><a class="ref" href="trees_2.html#D9">TREES_2:def 9</a></i>;<br/>
<b>hence </b><a NAME="E2:25"/>
for <font color="Olive">y</font> being   <a href="hidden.html#M1">set</a>   st <font color="Olive">y</font> <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K2">rng</a> <font color="Maroon">T</font> holds <br/><font color="Olive">y</font> is    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">D</font>
 ;<br/>


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