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<b>let </b><font color="Maroon">A</font> be   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font>;<br/>

<b>assume </b><a NAME="E1:109_1_1"/>
<font color="Maroon">A</font> is <a href="topgen_4.html#V5" target="_self">F_sigma</a>
 ;<br/>

<b>then consider </b><font color="Maroon">F</font> being  <a href="card_4.html#V1">countable</a> <a href="tops_2.html#V2">closed</a> <a href="struct_0.html#NM3">Subset-Family</a> of <font color="Maroon">T</font><b> such that </b><br/><a NAME="E3:109_1_1"/><i><font color="Green">E37</font></i>: 
<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="setfam_1.html#K5">union</a> <font color="Maroon">F</font>
 <b>by </b><i/>;<br/>
<a NAME="E4:109_1_1"/>
<font color="Maroon">F</font> <a href="tarski.html#R1">c=</a>  <a href="topgen_4.html#K5" target="_self">BorelSets</a> <font color="Maroon">T</font>
 
<b>by </b><i/>;<br/>
<a NAME="E5:109_1_1"/><b>then </b>
<font color="Maroon">A</font> <a href="hidden.html#R2">in</a>  <a href="topgen_4.html#K5" target="_self">BorelSets</a> <font color="Maroon">T</font>
 
<b>by </b><i><a class="ref" href="topgen_4.html#T5" target="_self">Th5</a>, </i>;<br/>
<b>hence </b><a NAME="E6:109_1_1"/>
<font color="Maroon">A</font> is <a href="topgen_4.html#V8" target="_self">Borel</a>
 <b>by </b><i/>;<br/>


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