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<b>let </b><font color="Maroon">c<sub>1</sub></font>, <font color="Maroon">c<sub>2</sub></font> be    <a href="hidden.html#M1">set</a> ;<br/>



<a NAME="E1:11"/>
<span class="p1">(<span class="default"><a href="trees_4.html#K1" target="_self">root-tree</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="funct_1.html#K1">.</a> <a href="xboole_0.html#K1">{}</a>  <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>1</sub></font>
 
<b>by </b><i><a class="ref" href="trees_4.html#T3" target="_self">Th3</a></i>;<br/>
<b>hence </b><a NAME="E2:11"/>
(  <a href="trees_4.html#K1" target="_self">root-tree</a> <font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R1">=</a>  <a href="trees_4.html#K1" target="_self">root-tree</a> <font color="Maroon">c<sub>2</sub></font> implies <font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>2</sub></font> )
 <b>by </b><i><a class="ref" href="trees_4.html#T3" target="_self">Th3</a></i>;<br/>


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