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<b>let </b><font color="Maroon">Omega</font> be  non <a href="xboole_0.html#V1">empty</a>  <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">D</font> be  non <a href="xboole_0.html#V1">empty</a> <a href="setfam_1.html#NM1">Subset-Family</a> of <font color="Maroon">Omega</font>;<br/>



<b>assume </b><a NAME="E1:28"/><i><font color="Green">E31</font></i>: 
( <font color="Maroon">D</font> is    <a href="dynkin.html#M1" target="_self">Dynkin_System</a> of <font color="Maroon">Omega</font> &amp; <font color="Maroon">D</font> is <a href="finsub_1.html#V2">intersection_stable</a> )
 ;<br/>

<b>let </b><font color="Maroon">x</font> be  <a href="finset_1.html#V1">finite</a>  <a href="hidden.html#M1">set</a> ;<br/>

<b>assume </b><a NAME="E2:28"/><i><font color="Green">E32</font></i>: 
<font color="Maroon">x</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">D</font>
 ;<br/>

<b>defpred </b><font color="Maroon">S<sub>1</sub></font>[   <a href="hidden.html#M1">set</a> ] <b>means </b> <a href="tarski.html#K3">union</a> <font color="Maroon">a<sub>1</sub></font> <a href="hidden.html#R2">in</a> <font color="Maroon">D</font>;<br/>
<a NAME="E3:28"/><i><font color="Green">E40</font></i>: 
<font color="Maroon">x</font> is <a href="finset_1.html#V1">finite</a>
 
;<br/>
<a NAME="E4:28"/><i><font color="Green">E41</font></i>: 
<font color="Maroon">S<sub>1</sub></font>[ <a href="xboole_0.html#K1">{}</a> ]
 
<b>by </b><i>, , <a class="ref" href="zfmisc_1.html#T2">ZFMISC_1:2</a></i>;<br/>
<a NAME="E5:28"/><i><font color="Green">E44</font></i>: 
for <font color="Olive">y</font>, <font color="Olive">b</font> being   <a href="hidden.html#M1">set</a>   st <font color="Olive">y</font> <a href="hidden.html#R2">in</a> <font color="Maroon">x</font> &amp; <font color="Olive">b</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">x</font> &amp; <font color="Maroon">S<sub>1</sub></font>[<font color="Olive">b</font>] holds <br/><font color="Maroon">S<sub>1</sub></font>[<font color="Olive">b</font> <a href="xboole_0.html#K2">\/</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default"><font color="Olive">y</font></span><a href="tarski.html#K1">}</a></span>]
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="28_1"><b>proof </b></a><div class="add">

<b>let </b><font color="Maroon">y</font> be    <a href="hidden.html#M1">set</a> , <font color="Maroon">b</font> be    <a href="hidden.html#M1">set</a> ;<br/>

<b>assume </b><a NAME="E1:28_1"/><i><font color="Green">E45</font></i>: 
( <font color="Maroon">y</font> <a href="hidden.html#R2">in</a> <font color="Maroon">x</font> &amp; <font color="Maroon">b</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">x</font> &amp;  <a href="tarski.html#K3">union</a> <font color="Maroon">b</font> <a href="hidden.html#R2">in</a> <font color="Maroon">D</font> )
 ;<br/>

<a NAME="E2:28_1"/><i><font color="Green">E46</font></i>: 
 <a href="tarski.html#K3">union</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default"><font color="Maroon">y</font></span><a href="tarski.html#K1">}</a></span> <a href="hidden.html#R1">=</a> <font color="Maroon">y</font>
 
<b>by </b><i><a class="ref" href="zfmisc_1.html#T31">ZFMISC_1:31</a></i>;<br/>
<b>reconsider </b><font color="Maroon">unionb</font> =  <a href="tarski.html#K3">union</a> <font color="Maroon">b</font> as   <a href="subset_1.html#NM2">Subset</a> of <font color="Maroon">Omega</font> <b>by </b><i/>;<br/>
<a NAME="E4:28_1"/>
<font color="Maroon">y</font> <a href="hidden.html#R2">in</a> <font color="Maroon">D</font>
 
<b>by </b><i>, </i>;<br/>
<b>then reconsider </b><font color="Maroon">y1</font> = <font color="Maroon">y</font> as   <a href="subset_1.html#NM2">Subset</a> of <font color="Maroon">Omega</font> ;<br/>
<a NAME="E6:28_1"/>
<font color="Maroon">unionb</font> <a href="subset_1.html#K4">\/</a> <font color="Maroon">y1</font> <a href="hidden.html#R2">in</a> <font color="Maroon">D</font>
 
<b>by </b><i>, , , </i>;<br/>
<b>hence </b><a NAME="E7:28_1"/>
 <a href="tarski.html#K3">union</a> <span class="p1">(<span class="default"><font color="Maroon">b</font> <a href="xboole_0.html#K2">\/</a> <span class="p2"><a href="tarski.html#K1">{</a><span class="default"><font color="Maroon">y</font></span><a href="tarski.html#K1">}</a></span></span>)</span> <a href="hidden.html#R2">in</a> <font color="Maroon">D</font>
 <b>by </b><i>, <a class="ref" href="zfmisc_1.html#T96">ZFMISC_1:96</a></i>;<br/>


</div><b>end;</b></div>
<b>thus </b><a NAME="E6:28"/>
<font color="Maroon">S<sub>1</sub></font>[<font color="Maroon">x</font>]
 <b>from </b><i><a class="ref" href="finset_1.html#S2">FINSET_1:sch 2</a>(, , );</i><br/>


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