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<b>let </b><font color="Maroon">c<sub>3</sub></font> be   <a href="closure2.html#NM1">SubsetFamily</a> of <font color="Maroon">c<sub>2</sub></font>;<br/>

<b>assume </b><a NAME="E1:48_1_1"/><i><font color="Green">E25</font></i>: 
<font color="Maroon">c<sub>3</sub></font> is <a href="closure2.html#V2" target="_self">absolutely-additive</a>
 ;<br/>

<b>reconsider </b><font color="Maroon">c<sub>4</sub></font> =  <a href="xboole_0.html#K1">{}</a>  as   <a href="closure2.html#NM1">SubsetFamily</a> of <font color="Maroon">c<sub>2</sub></font> <b>by </b><i><a class="ref" href="xboole_1.html#T2">XBOOLE_1:2</a></i>;<br/>
<a NAME="E3:48_1_1"/>
<span class="p1"><a href="closure2.html#K5" target="_self">|:</a><span class="default"><font color="Maroon">c<sub>4</sub></font></span><a href="closure2.html#K5" target="_self">:|</a></span> <a href="pboole.html#R6">=</a>  <a href="pboole.html#K1">[0]</a> <font color="Maroon">c<sub>1</sub></font>
 
<b>by </b><i><a class="ref" href="closure2.html#D4" target="_self">Def4</a></i>;<br/>
<a NAME="E4:48_1_1"/><b>then </b><i><font color="Green">E26</font></i>: 
 <a href="mboolean.html#K2">union</a> <span class="p1"><a href="closure2.html#K5" target="_self">|:</a><span class="default"><font color="Maroon">c<sub>4</sub></font></span><a href="closure2.html#K5" target="_self">:|</a></span> <a href="pboole.html#R6">=</a>  <a href="pboole.html#K1">[0]</a> <font color="Maroon">c<sub>1</sub></font>
 
<b>by </b><i><a class="ref" href="mboolean.html#T22">MBOOLEAN:22</a></i>;<br/>
<a NAME="E5:48_1_1"/>
<font color="Maroon">c<sub>4</sub></font> <a href="tarski.html#R1">c=</a> <font color="Maroon">c<sub>3</sub></font>
 
<b>by </b><i><a class="ref" href="xboole_1.html#T2">XBOOLE_1:2</a></i>;<br/>
<b>hence </b><a NAME="E6:48_1_1"/>
 <a href="pboole.html#K1">[0]</a> <font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R2">in</a> <font color="Maroon">c<sub>3</sub></font>
 <b>by </b><i><a class="txt" href="closure2.html#E1:48_1_1"><i><font color="Green">E25</font></i></a>, <a class="txt" href="closure2.html#E4:48_1_1"><i><font color="Green">E26</font></i></a>, <a class="ref" href="closure2.html#D6" target="_self">Def6</a></i>; <i><font color="Red">:: according to </font></i><a class="ref" href="closure2.html#D10" target="_self">CLOSURE2:def 10</a><br/>


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