<?xml version="1.0"?>
<div class="add">

<b>let </b><font color="Maroon">c<sub>1</sub></font> be   <a href="cat_1.html#NM4">Category</a>;<br/><b>let </b><font color="Maroon">c<sub>2</sub></font> be    <a href="hidden.html#M1">set</a> ;<br/>



<a NAME="E1:41"/>
<font color="Maroon">c<sub>1</sub></font> <a href="oppcat_1.html#K2">opp</a>  <a href="hidden.html#R1">=</a>  <a href="cat_1.html#G1">CatStr</a>(# the <a href="cat_1.html#U1">Objects</a> of <font color="Maroon">c<sub>1</sub></font>,the <a href="cat_1.html#U2">Morphisms</a> of <font color="Maroon">c<sub>1</sub></font>,the <a href="cat_1.html#U4">Cod</a> of <font color="Maroon">c<sub>1</sub></font>,the <a href="cat_1.html#U3">Dom</a> of <font color="Maroon">c<sub>1</sub></font>,<span class="p1">(<span class="default"><a href="oppcat_1.html#K1">~</a> the <a href="cat_1.html#U5">Comp</a> of <font color="Maroon">c<sub>1</sub></font></span>)</span>,the <a href="cat_1.html#U6">Id</a> of <font color="Maroon">c<sub>1</sub></font> #)
 
<b>by </b><i><a class="ref" href="oppcat_1.html#D1">OPPCAT_1:def 1</a></i>;<br/>
<b>hence </b><a NAME="E2:41"/>
( <font color="Maroon">c<sub>2</sub></font> is   <a href="index_1.html#NM10">coIndexing</a> of <font color="Maroon">c<sub>1</sub></font> iff <font color="Maroon">c<sub>2</sub></font> is   <a href="index_1.html#NM9">Indexing</a> of <span class="p1">(<span class="default"><font color="Maroon">c<sub>1</sub></font> <a href="oppcat_1.html#K2">opp</a> </span>)</span> )
 ;<br/>


</div>
