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<b>let </b><font color="Maroon">M</font> be   <a href="midsp_1.html#NM1">MidSp</a>;<br/><b>let </b><font color="Maroon">x</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">M</font>;<br/><b>let </b><font color="Maroon">a</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">M</font>;<br/><b>let </b><font color="Maroon">x'</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">M</font>;<br/>







<b>assume </b><a NAME="E1:15"/><i><font color="Green">E37</font></i>: 
<font color="Maroon">x</font> <a href="midsp_1.html#K4" target="_self">@</a> <font color="Maroon">a</font> <a href="hidden.html#R1">=</a> <font color="Maroon">x'</font> <a href="midsp_1.html#K4" target="_self">@</a> <font color="Maroon">a</font>
 ;<br/>

<b>consider </b><font color="Maroon">y</font> being   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">M</font><b> such that </b><br/><a NAME="E3:15"/><i><font color="Green">E38</font></i>: 
<font color="Maroon">y</font> <a href="midsp_1.html#K4" target="_self">@</a> <font color="Maroon">a</font> <a href="hidden.html#R1">=</a> <font color="Maroon">x</font>
 <b>by </b><i/>;<br/>
<font color="Maroon">x</font> = 
<font color="Maroon">x</font> <a href="midsp_1.html#K4" target="_self">@</a> <span class="p1">(<span class="default"><font color="Maroon">y</font> <a href="midsp_1.html#K4" target="_self">@</a> <font color="Maroon">a</font></span>)</span>
<b>by </b><i>, </i>
<br/>.= 
<span class="p1">(<span class="default"><font color="Maroon">x</font> <a href="midsp_1.html#K4" target="_self">@</a> <font color="Maroon">y</font></span>)</span> <a href="midsp_1.html#K4" target="_self">@</a> <span class="p1">(<span class="default"><font color="Maroon">x'</font> <a href="midsp_1.html#K4" target="_self">@</a> <font color="Maroon">a</font></span>)</span>
<b>by </b><i>, </i>
<br/>.= 
<font color="Maroon">x</font> <a href="midsp_1.html#K4" target="_self">@</a> <span class="p1">(<span class="default"><font color="Maroon">x</font> <a href="midsp_1.html#K4" target="_self">@</a> <font color="Maroon">x'</font></span>)</span>
<b>by </b><i>, </i>
;<br/>
<a NAME="E5:15"/><b>then </b>
<font color="Maroon">x</font> <a href="hidden.html#R1">=</a> <font color="Maroon">x</font> <a href="midsp_1.html#K4" target="_self">@</a> <font color="Maroon">x'</font>
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E6:15"/>
<font color="Maroon">x</font> <a href="hidden.html#R1">=</a> <font color="Maroon">x'</font>
 <b>by </b><i/>;<br/>


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