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<b>let </b><font color="Maroon">c<sub>1</sub></font>, <font color="Maroon">c<sub>2</sub></font> be  non <a href="xboole_0.html#V1">empty</a> <a href="finsub_1.html#V4">preBoolean</a>  <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">c<sub>3</sub></font>, <font color="Maroon">c<sub>4</sub></font>, <font color="Maroon">c<sub>5</sub></font> be    <a href="subset_1.html#M1">Element</a> of <span class="p1"><a href="zfmisc_1.html#K2">[:</a><span class="default"><font color="Maroon">c<sub>1</sub></font>,<font color="Maroon">c<sub>2</sub></font></span><a href="zfmisc_1.html#K2">:]</a></span>;<br/>









<b>assume </b><a NAME="E1:10"/>
( <font color="Maroon">c<sub>3</sub></font> <a href="domain_1.html#K2">`1</a>  <a href="tarski.html#R1">c=</a> <font color="Maroon">c<sub>4</sub></font> <a href="domain_1.html#K2">`1</a>  &amp; <font color="Maroon">c<sub>3</sub></font> <a href="domain_1.html#K3">`2</a>  <a href="tarski.html#R1">c=</a> <font color="Maroon">c<sub>4</sub></font> <a href="domain_1.html#K3">`2</a>  &amp; <font color="Maroon">c<sub>5</sub></font> <a href="domain_1.html#K2">`1</a>  <a href="tarski.html#R1">c=</a> <font color="Maroon">c<sub>4</sub></font> <a href="domain_1.html#K2">`1</a>  &amp; <font color="Maroon">c<sub>5</sub></font> <a href="domain_1.html#K3">`2</a>  <a href="tarski.html#R1">c=</a> <font color="Maroon">c<sub>4</sub></font> <a href="domain_1.html#K3">`2</a>  )
 ; <i><font color="Red">:: according to </font></i><a class="ref" href="normform.html#D1" target="_self">NORMFORM:def 1</a><br/>

<a NAME="E2:10"/><b>then </b>
( <span class="p1">(<span class="default"><font color="Maroon">c<sub>3</sub></font> <a href="domain_1.html#K2">`1</a> </span>)</span> <a href="finsub_1.html#K1">\/</a> <span class="p1">(<span class="default"><font color="Maroon">c<sub>5</sub></font> <a href="domain_1.html#K2">`1</a> </span>)</span> <a href="tarski.html#R1">c=</a> <font color="Maroon">c<sub>4</sub></font> <a href="domain_1.html#K2">`1</a>  &amp; <span class="p1">(<span class="default"><font color="Maroon">c<sub>3</sub></font> <a href="domain_1.html#K3">`2</a> </span>)</span> <a href="finsub_1.html#K1">\/</a> <span class="p1">(<span class="default"><font color="Maroon">c<sub>5</sub></font> <a href="domain_1.html#K3">`2</a> </span>)</span> <a href="tarski.html#R1">c=</a> <font color="Maroon">c<sub>4</sub></font> <a href="domain_1.html#K3">`2</a>  )
 
<b>by </b><i><a class="ref" href="xboole_1.html#T8">XBOOLE_1:8</a></i>;<br/>
<b>hence </b><a NAME="E3:10"/>
( <span class="p1">(<span class="default"><font color="Maroon">c<sub>3</sub></font> <a href="normform.html#K1" target="_self">\/</a> <font color="Maroon">c<sub>5</sub></font></span>)</span> <a href="domain_1.html#K2">`1</a>  <a href="tarski.html#R1">c=</a> <font color="Maroon">c<sub>4</sub></font> <a href="domain_1.html#K2">`1</a>  &amp; <span class="p1">(<span class="default"><font color="Maroon">c<sub>3</sub></font> <a href="normform.html#K1" target="_self">\/</a> <font color="Maroon">c<sub>5</sub></font></span>)</span> <a href="domain_1.html#K3">`2</a>  <a href="tarski.html#R1">c=</a> <font color="Maroon">c<sub>4</sub></font> <a href="domain_1.html#K3">`2</a>  )
 <b>by </b><i><a class="ref" href="normform.html#T10" target="_self">Th10</a></i>; <i><font color="Red">:: according to </font></i><a class="ref" href="normform.html#D1" target="_self">NORMFORM:def 1</a><br/>


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