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



<a NAME="E1:52"/><i><font color="Green">E20</font></i>: 
 <a href="cat_1.html#K6" target="_self">Hom</a> <font color="Maroon">b</font>,<font color="Maroon">b</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a> 
 
<b>by </b><i/>;<br/>
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="52_1"><b>now </b></a><div class="add"><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>let </b><font color="Maroon">f1</font> be    <a href="cat_1.html#M1" target="_self">Morphism</a> of <font color="Maroon">a</font>,<font color="Maroon">b</font>, <font color="Maroon">f2</font> be    <a href="cat_1.html#M1" target="_self">Morphism</a> of <font color="Maroon">a</font>,<font color="Maroon">b</font>;<br/><b>assume </b><a NAME="E1:52_1"/>
 <a href="cat_1.html#K6" target="_self">Hom</a> <font color="Maroon">a</font>,<font color="Maroon">b</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a> 
 ;<br/><a NAME="E2:52_1"/><b>then </b>
( <span class="p1">(<span class="default"><a href="cat_1.html#K10" target="_self">id</a> <font color="Maroon">b</font></span>)</span> <a href="cat_1.html#K9" target="_self">*</a> <font color="Maroon">f1</font> <a href="hidden.html#R1">=</a> <font color="Maroon">f1</font> &amp; <span class="p1">(<span class="default"><a href="cat_1.html#K10" target="_self">id</a> <font color="Maroon">b</font></span>)</span> <a href="cat_1.html#K9" target="_self">*</a> <font color="Maroon">f2</font> <a href="hidden.html#R1">=</a> <font color="Maroon">f2</font> )
 <b>by </b><i/>;<br/><b>hence </b><a NAME="E3:52_1"/>
( <span class="p1">(<span class="default"><a href="cat_1.html#K10" target="_self">id</a> <font color="Maroon">b</font></span>)</span> <a href="cat_1.html#K9" target="_self">*</a> <font color="Maroon">f1</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><a href="cat_1.html#K10" target="_self">id</a> <font color="Maroon">b</font></span>)</span> <a href="cat_1.html#K9" target="_self">*</a> <font color="Maroon">f2</font> implies <font color="Maroon">f1</font> <a href="hidden.html#R1">=</a> <font color="Maroon">f2</font> )
 ;<br/></div><b>end;</b></div>
<b>hence </b><a NAME="E3:52"/>
 <a href="cat_1.html#K10" target="_self">id</a> <font color="Maroon">b</font> is <a href="cat_1.html#V3" target="_self">monic</a>
 <b>by </b><i>, <a class="ref" href="cat_1.html#D4" target="_self">Def4</a></i>;<br/>


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