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<b>let </b><font color="Maroon">c<sub>1</sub></font> be   <a href="trees_2.html#NM4">DecoratedTree</a>;<br/><b>let </b><font color="Maroon">c<sub>2</sub></font> be  non <a href="xboole_0.html#V1">empty</a> <a href="trees_3.html#V3">constituted-DTrees</a>  <a href="hidden.html#M1">set</a> ;<br/>



<b>assume </b><a NAME="E1:54"/>
<font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R2">in</a> <font color="Maroon">c<sub>2</sub></font>
 ;<br/>

<b>then reconsider </b><font color="Maroon">c<sub>3</sub></font> = <font color="Maroon">c<sub>1</sub></font> as    <a href="trees_3.html#M3">Element</a> of <font color="Maroon">c<sub>2</sub></font> ;<br/>
<b>reconsider </b><font color="Maroon">c<sub>4</sub></font> =  <a href="xboole_0.html#K1">{}</a>  as   <a href="trees_4.html#NM1">Node</a> of <font color="Maroon">c<sub>3</sub></font> <b>by </b><i><a class="ref" href="trees_1.html#T47">TREES_1:47</a></i>;<br/>
<a NAME="E4:54"/>
<font color="Maroon">c<sub>3</sub></font> <a href="trees_2.html#K5">|</a> <font color="Maroon">c<sub>4</sub></font> <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>3</sub></font>
 
<b>by </b><i><a class="ref" href="trees_9.html#T1" target="_self">Th1</a></i>;<br/>
<b>hence </b><a NAME="E5:54"/>
<font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R2">in</a>  <a href="trees_9.html#K9" target="_self">Subtrees</a> <font color="Maroon">c<sub>2</sub></font>
 ;<br/>


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