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<b>let </b><font color="Maroon">A</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#NM4">Category</a>;<br/><b>let </b><font color="Maroon">F1</font> be    <a href="cat_1.html#M2">Functor</a> of <font color="Maroon">A</font>,<font color="Maroon">B</font>, <font color="Maroon">F2</font> be    <a href="cat_1.html#M2">Functor</a> of <font color="Maroon">A</font>,<font color="Maroon">B</font>;<br/>





<b>assume </b><a NAME="E1:5"/><i><font color="Green">E18</font></i>: 
<font color="Maroon">F1</font> <a href="nattra_1.html#R1">is_transformable_to</a> <font color="Maroon">F2</font>
 ;<br/>

<b>let </b><font color="Maroon">t</font> be    <a href="nattra_1.html#M1">transformation</a> of <font color="Maroon">F1</font>,<font color="Maroon">F2</font>;<br/>

<b>assume </b><a NAME="E2:5"/><i><font color="Green">E19</font></i>: 
<font color="Maroon">t</font> is <a href="nattra_1.html#V1">invertible</a>
 ;<br/>

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

<b>thus </b><a NAME="E3:5"/>
 <a href="cat_1.html#K6">Hom</a> <span class="p1">(<span class="default"><font color="Maroon">F1</font> <a href="cat_1.html#K13">.</a> <font color="Maroon">a</font></span>)</span>,<span class="p1">(<span class="default"><font color="Maroon">F2</font> <a href="cat_1.html#K13">.</a> <font color="Maroon">a</font></span>)</span> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a> 
 <b>by </b><i>, <a class="ref" href="nattra_1.html#D2">NATTRA_1:def 2</a></i>; <i><font color="Red">:: according to </font></i><a class="ref" href="cat_1.html#D17">CAT_1:def 17</a><br/>

<a NAME="E4:5"/>
<font color="Maroon">t</font> <a href="nattra_1.html#K5">.</a> <font color="Maroon">a</font> is <a href="cat_1.html#V5">invertible</a>
 
<b>by </b><i>, <a class="ref" href="nattra_1.html#D10">NATTRA_1:def 10</a></i>;<br/>
<b>hence </b><a NAME="E5:5"/>
 ex <font color="Olive">b<sub>1</sub></font> being   <a href="cat_1.html#M1">Morphism</a> of <font color="Maroon">F1</font> <a href="cat_1.html#K13">.</a> <font color="Maroon">a</font>,<font color="Maroon">F2</font> <a href="cat_1.html#K13">.</a> <font color="Maroon">a</font> st <font color="Olive">b<sub>1</sub></font> is <a href="cat_1.html#V5">invertible</a>
 ;<br/>


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