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<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/>



<div><i><font color="Green">E21</font></i>: <a class="txt" onclick="hs2(this)" href="javascript:()" title="22_1"><b>now </b></a><div class="add"><b>assume </b><a NAME="E1:22_1"/>
<font color="Maroon">c<sub>1</sub></font> <a href="cqc_the3.html#R4" target="_self">|-|</a> <font color="Maroon">c<sub>2</sub></font>
 ;<br/><a NAME="E2:22_1"/><b>then </b>
( <font color="Maroon">c<sub>1</sub></font> <a href="cqc_the3.html#R2" target="_self">|-</a> <font color="Maroon">c<sub>2</sub></font> &amp; <font color="Maroon">c<sub>2</sub></font> <a href="cqc_the3.html#R2" target="_self">|-</a> <font color="Maroon">c<sub>1</sub></font> )
 <b>by </b><i><a class="ref" href="cqc_the3.html#T18" target="_self">Th18</a></i>;<br/><a NAME="E3:22_1"/><b>then </b>
( <font color="Maroon">c<sub>2</sub></font> <a href="tarski.html#R1">c=</a>  <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>1</sub></font> &amp; <font color="Maroon">c<sub>1</sub></font> <a href="tarski.html#R1">c=</a>  <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>2</sub></font> )
 <b>by </b><i><a class="ref" href="cqc_the3.html#T7" target="_self">Th7</a></i>;<br/><a NAME="E4:22_1"/><b>then </b>
(  <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>2</sub></font> <a href="tarski.html#R1">c=</a>  <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>1</sub></font> &amp;  <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>1</sub></font> <a href="tarski.html#R1">c=</a>  <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>2</sub></font> )
 <b>by </b><i><a class="ref" href="cqc_the3.html#T2" target="_self">Th2</a></i>;<br/><b>hence </b><a NAME="E5:22_1"/>
 <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R1">=</a>  <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>2</sub></font>
 <b>by </b><i><a class="ref" href="xboole_0.html#D10">XBOOLE_0:def 10</a></i>;<br/></div><b>end;</b></div>
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="22_2"><b>now </b></a><div class="add"><b>assume </b><a NAME="E1:22_2"/><i><font color="Green">E22</font></i>: 
 <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R1">=</a>  <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>2</sub></font>
 ;<br/><a NAME="E2:22_2"/>
( <font color="Maroon">c<sub>2</sub></font> <a href="tarski.html#R1">c=</a>  <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>2</sub></font> &amp; <font color="Maroon">c<sub>1</sub></font> <a href="tarski.html#R1">c=</a>  <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>1</sub></font> )
 <b>by </b><i><a class="ref" href="cqc_the1.html#T38">CQC_THE1:38</a></i>;<br/><a NAME="E3:22_2"/><b>then </b>
( <font color="Maroon">c<sub>1</sub></font> <a href="cqc_the3.html#R2" target="_self">|-</a> <font color="Maroon">c<sub>2</sub></font> &amp; <font color="Maroon">c<sub>2</sub></font> <a href="cqc_the3.html#R2" target="_self">|-</a> <font color="Maroon">c<sub>1</sub></font> )
 <b>by </b><i><a class="txt" href="cqc_the3.html#E1:22_2"><i><font color="Green">E22</font></i></a>, <a class="ref" href="cqc_the3.html#T7" target="_self">Th7</a></i>;<br/><b>hence </b><a NAME="E4:22_2"/>
<font color="Maroon">c<sub>1</sub></font> <a href="cqc_the3.html#R4" target="_self">|-|</a> <font color="Maroon">c<sub>2</sub></font>
 <b>by </b><i><a class="ref" href="cqc_the3.html#T18" target="_self">Th18</a></i>;<br/></div><b>end;</b></div>
<b>hence </b><a NAME="E3:22"/>
( <font color="Maroon">c<sub>1</sub></font> <a href="cqc_the3.html#R4" target="_self">|-|</a> <font color="Maroon">c<sub>2</sub></font> iff  <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R1">=</a>  <a href="cqc_the1.html#K1">Cn</a> <font color="Maroon">c<sub>2</sub></font> )
 <b>by </b><i><a class="txt" href="cqc_the3.html#E1:22"><i><font color="Green">E21</font></i></a></i>;<br/>


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