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<b>let </b><font color="Maroon">X1</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> , <font color="Maroon">X2</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><b>that </b><br/><a NAME="E1:18"/><i><font color="Green">E36</font></i>: 
for <font color="Olive">t</font> being   <a href="trees_3.html#M3">Element</a> of <font color="Maroon">X1</font> holds  <font color="Olive">t</font> is <a href="finset_1.html#V1">finite</a>
 <b>and </b><br/><a NAME="E2:18"/><i><font color="Green">E39</font></i>: 
for <font color="Olive">t</font> being   <a href="trees_3.html#M3">Element</a> of <font color="Maroon">X2</font> holds  <font color="Olive">t</font> is <a href="finset_1.html#V1">finite</a>
 ;<br/>

<div><i><font color="Green">E42</font></i>: <a class="txt" onclick="hs2(this)" href="javascript:()" title="18_1"><b>now </b></a><div class="add"><b>let </b><font color="Maroon">t</font> be    <a href="trees_3.html#M3">Element</a> of <font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font>;<br/><a NAME="E1:18_1"/>
( <font color="Maroon">t</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X1</font> or <font color="Maroon">t</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X2</font> )
 <b>by </b><i><a class="ref" href="xboole_0.html#D2">XBOOLE_0:def 2</a></i>;<br/><b>hence </b><a NAME="E2:18_1"/>
<font color="Maroon">t</font> is <a href="finset_1.html#V1">finite</a>
 <b>by </b><i>, </i>;<br/></div><b>end;</b></div>
<b>let </b><font color="Maroon">C</font> be    <a href="hidden.html#M1">set</a> ;<br/>

<b>set </b><font color="Maroon">X</font> = <font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font>;<br/>
<b>set </b><font color="Maroon">f</font> = <font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <span class="p1">(<span class="default"><font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font></span>)</span>;<br/>
<b>set </b><font color="Maroon">f1</font> = <font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X1</font>;<br/>
<b>set </b><font color="Maroon">f2</font> = <font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X2</font>;<br/>
<a NAME="E4:18"/><i><font color="Green">E65</font></i>: 
(  <a href="relat_1.html#K1">dom</a> <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <span class="p2">(<span class="default"><font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font></span>)</span></span>)</span> <a href="hidden.html#R1">=</a> <font color="Maroon">C</font> <a href="trees_9.html#K12">-Subtrees</a> <span class="p1">(<span class="default"><font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font></span>)</span> &amp;  <a href="relat_1.html#K1">dom</a> <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X1</font></span>)</span> <a href="hidden.html#R1">=</a> <font color="Maroon">C</font> <a href="trees_9.html#K12">-Subtrees</a> <font color="Maroon">X1</font> &amp;  <a href="relat_1.html#K1">dom</a> <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X2</font></span>)</span> <a href="hidden.html#R1">=</a> <font color="Maroon">C</font> <a href="trees_9.html#K12">-Subtrees</a> <font color="Maroon">X2</font> )
 
<b>by </b><i><a class="ref" href="funct_2.html#D1">FUNCT_2:def 1</a></i>;<br/>
<a NAME="E5:18"/><i><font color="Green">E71</font></i>: 
<font color="Maroon">C</font> <a href="trees_9.html#K12">-Subtrees</a> <span class="p1">(<span class="default"><font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font></span>)</span> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K12">-Subtrees</a> <font color="Maroon">X1</font></span>)</span> <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K12">-Subtrees</a> <font color="Maroon">X2</font></span>)</span>
 
<b>by </b><i/>;<br/>
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="18_2"><b>now </b></a><div class="add"><b>let </b><font color="Maroon">x</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>assume </b><a NAME="E1:18_2"/><i><font color="Green">E72</font></i>: 
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <span class="p1">(<span class="default"><a href="relat_1.html#K1">dom</a> <span class="p2">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X1</font></span>)</span></span>)</span> <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><a href="relat_1.html#K1">dom</a> <span class="p2">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X2</font></span>)</span></span>)</span>
 ;<br/><b>then reconsider </b><font color="Maroon">t</font> = <font color="Maroon">x</font> as    <a href="trees_3.html#M3">Element</a> of  <a href="trees_9.html#K9">Subtrees</a> <span class="p1">(<span class="default"><font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font></span>)</span> <b>by </b><i>, </i>;<br/><a NAME="E3:18_2"/>
<span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <span class="p2">(<span class="default"><font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font></span>)</span></span>)</span> <a href="funct_1.html#K1">.</a> <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <span class="p1">(<span class="default"><a href="trees_9.html#K9">Subtrees</a> <span class="p2">(<span class="default"><font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font></span>)</span></span>)</span> <a href="finseq_1.html#K13">*</a> 
 <b>by </b><i>, , , <a class="ref" href="funct_2.html#T7">FUNCT_2:7</a></i>;<br/><b>then reconsider </b><font color="Maroon">p</font> = <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <span class="p2">(<span class="default"><font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font></span>)</span></span>)</span> <a href="funct_1.html#K1">.</a> <font color="Maroon">x</font> as    <a href="finseq_1.html#M2">FinSequence</a> of  <a href="trees_9.html#K9">Subtrees</a> <span class="p1">(<span class="default"><font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font></span>)</span> <b>by </b><i><a class="ref" href="finseq_1.html#D11">FINSEQ_1:def 11</a></i>;<br/><div><b>hereby </b>
<div class="add"><b>assume </b><a NAME="E1:18_2_1"/><i><font color="Green">E73</font></i>: 
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K1">dom</a> <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X2</font></span>)</span>
 ;<br/><a NAME="E2:18_2_1"/><b>then </b>
<span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X2</font></span>)</span> <a href="funct_1.html#K1">.</a> <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <span class="p1">(<span class="default"><a href="trees_9.html#K9">Subtrees</a> <font color="Maroon">X2</font></span>)</span> <a href="finseq_1.html#K13">*</a> 
 <b>by </b><i>, <a class="ref" href="funct_2.html#T7">FUNCT_2:7</a></i>;<br/><b>then reconsider </b><font color="Maroon">p2</font> = <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X2</font></span>)</span> <a href="funct_1.html#K1">.</a> <font color="Maroon">x</font> as    <a href="finseq_1.html#M2">FinSequence</a> of  <a href="trees_9.html#K9">Subtrees</a> <font color="Maroon">X2</font> <b>by </b><i><a class="ref" href="finseq_1.html#D11">FINSEQ_1:def 11</a></i>;<br/><a NAME="E4:18_2_1"/>
( <font color="Maroon">t</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><font color="Maroon">t</font> <a href="funct_1.html#K1">.</a> <a href="xboole_0.html#K1">{}</a> </span>)</span> <a href="trees_4.html#K4">-tree</a> <font color="Maroon">p</font> &amp; <font color="Maroon">t</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><font color="Maroon">t</font> <a href="funct_1.html#K1">.</a> <a href="xboole_0.html#K1">{}</a> </span>)</span> <a href="trees_4.html#K4">-tree</a> <font color="Maroon">p2</font> )
 <b>by </b><i>, , , , , , <a class="ref" href="trees_9.html#D13">TREES_9:def 13</a></i>;<br/><b>hence </b><a NAME="E5:18_2_1"/>
<span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <span class="p2">(<span class="default"><font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font></span>)</span></span>)</span> <a href="funct_1.html#K1">.</a> <font color="Maroon">x</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X2</font></span>)</span> <a href="funct_1.html#K1">.</a> <font color="Maroon">x</font>
 <b>by </b><i><a class="ref" href="trees_4.html#T15">TREES_4:15</a></i>;<br/></div>
<b>end;</b></div><b>assume </b><a NAME="E6:18_2"/>
not <font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K1">dom</a> <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X2</font></span>)</span>
 ;<br/><a NAME="E7:18_2"/><b>then </b><i><font color="Green">E75</font></i>: 
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K1">dom</a> <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X1</font></span>)</span>
 <b>by </b><i>, <a class="ref" href="xboole_0.html#D2">XBOOLE_0:def 2</a></i>;<br/><a NAME="E8:18_2"/><b>then </b>
<span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X1</font></span>)</span> <a href="funct_1.html#K1">.</a> <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <span class="p1">(<span class="default"><a href="trees_9.html#K9">Subtrees</a> <font color="Maroon">X1</font></span>)</span> <a href="finseq_1.html#K13">*</a> 
 <b>by </b><i>, <a class="ref" href="funct_2.html#T7">FUNCT_2:7</a></i>;<br/><b>then reconsider </b><font color="Maroon">p1</font> = <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X1</font></span>)</span> <a href="funct_1.html#K1">.</a> <font color="Maroon">x</font> as    <a href="finseq_1.html#M2">FinSequence</a> of  <a href="trees_9.html#K9">Subtrees</a> <font color="Maroon">X1</font> <b>by </b><i><a class="ref" href="finseq_1.html#D11">FINSEQ_1:def 11</a></i>;<br/><a NAME="E10:18_2"/>
( <font color="Maroon">t</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><font color="Maroon">t</font> <a href="funct_1.html#K1">.</a> <a href="xboole_0.html#K1">{}</a> </span>)</span> <a href="trees_4.html#K4">-tree</a> <font color="Maroon">p</font> &amp; <font color="Maroon">t</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><font color="Maroon">t</font> <a href="funct_1.html#K1">.</a> <a href="xboole_0.html#K1">{}</a> </span>)</span> <a href="trees_4.html#K4">-tree</a> <font color="Maroon">p1</font> )
 <b>by </b><i>, , , , , , <a class="ref" href="trees_9.html#D13">TREES_9:def 13</a></i>;<br/><b>hence </b><a NAME="E11:18_2"/>
<span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <span class="p2">(<span class="default"><font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font></span>)</span></span>)</span> <a href="funct_1.html#K1">.</a> <font color="Maroon">x</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X1</font></span>)</span> <a href="funct_1.html#K1">.</a> <font color="Maroon">x</font>
 <b>by </b><i><a class="ref" href="trees_4.html#T15">TREES_4:15</a></i>;<br/></div><b>end;</b></div>
<b>hence </b><a NAME="E7:18"/>
<font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <span class="p1">(<span class="default"><font color="Maroon">X1</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">X2</font></span>)</span> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X1</font></span>)</span> <a href="funct_4.html#K1">+*</a> <span class="p1">(<span class="default"><font color="Maroon">C</font> <a href="trees_9.html#K13">-ImmediateSubtrees</a> <font color="Maroon">X2</font></span>)</span>
 <b>by </b><i>, , <a class="ref" href="funct_4.html#D1">FUNCT_4:def 1</a></i>;<br/>


</div>
