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<b>consider </b><font color="Maroon">xx1</font> being    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">X1</font>, <font color="Maroon">xx2</font> being    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">X2</font>, <font color="Maroon">xx3</font> being    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">X3</font>, <font color="Maroon">xx4</font> being    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">X4</font><b> such that </b><br/><a NAME="E2:58_4_2"/><i><font color="Green">E56</font></i>: 
<font color="Maroon">x</font> <a href="hidden.html#R1">=</a> <span class="p1"><a href="mcart_1.html#K4" target="_self">[</a><span class="default"><font color="Maroon">xx1</font>,<font color="Maroon">xx2</font>,<font color="Maroon">xx3</font>,<font color="Maroon">xx4</font></span><a href="mcart_1.html#K4" target="_self">]</a></span>
 <b>by </b><i>, </i>;<br/>
<b>let </b><font color="Maroon">y</font> be    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">X4</font>, <font color="Maroon">z</font> be    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">X4</font>;<br/>

<b>assume </b><a NAME="E3:58_4_2"/>
for <font color="Olive">x1</font>, <font color="Olive">x2</font>, <font color="Olive">x3</font>, <font color="Olive">x4</font> being   <a href="hidden.html#M1">set</a>   st <font color="Maroon">x</font> <a href="hidden.html#R1">=</a> <span class="p1"><a href="mcart_1.html#K4" target="_self">[</a><span class="default"><font color="Olive">x1</font>,<font color="Olive">x2</font>,<font color="Olive">x3</font>,<font color="Olive">x4</font></span><a href="mcart_1.html#K4" target="_self">]</a></span> holds <br/><font color="Maroon">y</font> <a href="hidden.html#R1">=</a> <font color="Olive">x4</font>
 ;<br/>

<a NAME="E4:58_4_2"/><b>then </b><i><font color="Green">E57</font></i>: 
<font color="Maroon">y</font> <a href="hidden.html#R1">=</a> <font color="Maroon">xx4</font>
 
<b>by </b><i/>;<br/>
<b>assume </b><a NAME="E5:58_4_2"/>
for <font color="Olive">x1</font>, <font color="Olive">x2</font>, <font color="Olive">x3</font>, <font color="Olive">x4</font> being   <a href="hidden.html#M1">set</a>   st <font color="Maroon">x</font> <a href="hidden.html#R1">=</a> <span class="p1"><a href="mcart_1.html#K4" target="_self">[</a><span class="default"><font color="Olive">x1</font>,<font color="Olive">x2</font>,<font color="Olive">x3</font>,<font color="Olive">x4</font></span><a href="mcart_1.html#K4" target="_self">]</a></span> holds <br/><font color="Maroon">z</font> <a href="hidden.html#R1">=</a> <font color="Olive">x4</font>
 ;<br/>

<b>hence </b><a NAME="E6:58_4_2"/>
<font color="Maroon">y</font> <a href="hidden.html#R1">=</a> <font color="Maroon">z</font>
 <b>by </b><i>, <a class="ref" href="mcart_1.html#T1" target="_self">Th1</a></i>;<br/>


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