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

<b>let </b><font color="Maroon">c<sub>1</sub></font>, <font color="Maroon">c<sub>2</sub></font> be   <a href="subset_1.html#NM2">Subset</a> of <a href="cqc_lang.html#K7">CQC-WFF</a> ;<br/>



<a NAME="E1:25"/>
<font color="Maroon">c<sub>1</sub></font> <a href="subset_1.html#K4">\/</a> <font color="Maroon">c<sub>2</sub></font> <a href="tarski.html#R1">c=</a> <span class="p1">(<span class="default"><a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="subset_1.html#K4">\/</a> <span class="p1">(<span class="default"><a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>2</sub></font></span>)</span>
 
<b>by </b><i><a class="txt" href="cqc_the3.html#E25"><i><font color="Green">Lemma21</font></i></a></i>;<br/>
<a NAME="E2:25"/><b>then </b><i><font color="Green">E24</font></i>: 
 <a href="cqc_the1.html#K1">Cn</a> <span class="p1">(<span class="default"><font color="Maroon">c<sub>1</sub></font> <a href="subset_1.html#K4">\/</a> <font color="Maroon">c<sub>2</sub></font></span>)</span> <a href="tarski.html#R1">c=</a>  <a href="cqc_the1.html#K1">Cn</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="subset_1.html#K4">\/</a> <span class="p2">(<span class="default"><a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>2</sub></font></span>)</span></span>)</span>
 
<b>by </b><i><a class="ref" href="cqc_the1.html#T39">CQC_THE1:39</a></i>;<br/>
<a NAME="E3:25"/>
<span class="p1">(<span class="default"><a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="subset_1.html#K4">\/</a> <span class="p1">(<span class="default"><a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>2</sub></font></span>)</span> <a href="tarski.html#R1">c=</a>  <a href="cqc_the1.html#K1">Cn</a> <span class="p1">(<span class="default"><font color="Maroon">c<sub>1</sub></font> <a href="subset_1.html#K4">\/</a> <font color="Maroon">c<sub>2</sub></font></span>)</span>
 
<b>by </b><i><a class="ref" href="cqc_the3.html#T21" target="_self">Th21</a></i>;<br/>
<a NAME="E4:25"/><b>then </b>
 <a href="cqc_the1.html#K1">Cn</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="subset_1.html#K4">\/</a> <span class="p2">(<span class="default"><a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>2</sub></font></span>)</span></span>)</span> <a href="tarski.html#R1">c=</a>  <a href="cqc_the1.html#K1">Cn</a> <span class="p1">(<span class="default"><font color="Maroon">c<sub>1</sub></font> <a href="subset_1.html#K4">\/</a> <font color="Maroon">c<sub>2</sub></font></span>)</span>
 
<b>by </b><i><a class="ref" href="cqc_the3.html#T2" target="_self">Th2</a></i>;<br/>
<b>hence </b><a NAME="E5:25"/>
 <a href="cqc_the1.html#K1">Cn</a> <span class="p1">(<span class="default"><font color="Maroon">c<sub>1</sub></font> <a href="subset_1.html#K4">\/</a> <font color="Maroon">c<sub>2</sub></font></span>)</span> <a href="hidden.html#R1">=</a>  <a href="cqc_the1.html#K1">Cn</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="subset_1.html#K4">\/</a> <span class="p2">(<span class="default"><a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>2</sub></font></span>)</span></span>)</span>
 <b>by </b><i><a class="txt" href="cqc_the3.html#E2:25"><i><font color="Green">E24</font></i></a>, <a class="ref" href="xboole_0.html#D10">XBOOLE_0:def 10</a></i>;<br/>


</div>
