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<b>let </b><font color="Maroon">C</font> be   <a href="cat_1.html#NM4">Category</a>;<br/><b>let </b><font color="Maroon">a</font> be   <a href="cat_1.html#NM1">Object</a> of <font color="Maroon">C</font>;<br/>



<b>thus </b><a NAME="E1:77"/><i><font color="Green">E20</font></i>: 
 <a href="cat_1.html#K6" target="_self">Hom</a> <font color="Maroon">a</font>,<font color="Maroon">a</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a> 
 <b>by </b><i/>; <i><font color="Red">:: according to </font></i><a class="ref" href="cat_1.html#D17" target="_self">CAT_1:def 17</a><br/>

<b>take </b>
 <a href="cat_1.html#K10" target="_self">id</a> <font color="Maroon">a</font>
;<br/>

<a NAME="E2:77"/>
<span class="p1">(<span class="default"><a href="cat_1.html#K10" target="_self">id</a> <font color="Maroon">a</font></span>)</span> <a href="cat_1.html#K9" target="_self">*</a> <span class="p1">(<span class="default"><a href="cat_1.html#K10" target="_self">id</a> <font color="Maroon">a</font></span>)</span> <a href="hidden.html#R1">=</a>  <a href="cat_1.html#K10" target="_self">id</a> <font color="Maroon">a</font>
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E3:77"/>
 <a href="cat_1.html#K10" target="_self">id</a> <font color="Maroon">a</font> is <a href="cat_1.html#V5" target="_self">invertible</a>
 <b>by </b><i>, <a class="ref" href="cat_1.html#T18" target="_self">Th18</a></i>;<br/>


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