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<b>let </b><font color="Maroon">I</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">Y</font> be    <a href="pboole.html#M1" target="_self">ManySortedSet</a> of <font color="Maroon">I</font>;<br/><b>let </b><font color="Maroon">X</font> be    <a href="pboole.html#M1" target="_self">ManySortedSet</a> of <font color="Maroon">I</font>;<br/>





<b>assume </b><b>that </b><br/><a NAME="E1:139"/><i><font color="Green">E24</font></i>: 
<font color="Maroon">Y</font> is <a href="relat_1.html#V3">empty-yielding</a>
 <b>and </b><br/><a NAME="E2:139"/><i><font color="Green">E25</font></i>: 
<font color="Maroon">X</font> <a href="pboole.html#R2" target="_self">c=</a> <font color="Maroon">Y</font>
 ;<br/>

<b>let </b><font color="Maroon">i</font> be    <a href="hidden.html#M1">set</a> ; <i><font color="Red">:: according to </font></i><a class="ref" href="pboole.html#D15" target="_self">PBOOLE:def 15</a><br/>

<b>assume </b><a NAME="E3:139"/><i><font color="Green">E26</font></i>: 
<font color="Maroon">i</font> <a href="hidden.html#R2">in</a> <font color="Maroon">I</font>
 ;<br/>

<a NAME="E4:139"/><b>then </b><i><font color="Green">E27</font></i>: 
<font color="Maroon">X</font> <a href="funct_1.html#K1">.</a> <font color="Maroon">i</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">Y</font> <a href="funct_1.html#K1">.</a> <font color="Maroon">i</font>
 
<b>by </b><i><a class="ref" href="pboole.html#T21" target="_self">Th21</a>, </i>;<br/>
<a NAME="E5:139"/>
<font color="Maroon">Y</font> <a href="funct_1.html#K1">.</a> <font color="Maroon">i</font> is <a href="xboole_0.html#V1">empty</a>
 
<b>by </b><i><a class="ref" href="pboole.html#T19" target="_self">Th19</a>, <a class="ref" href="pboole.html#T22" target="_self">Th22</a>, <a class="ref" href="pboole.html#T17" target="_self">Th17</a></i>;<br/>
<b>hence </b><a NAME="E6:139"/>
<font color="Maroon">X</font> <a href="funct_1.html#K1">.</a> <font color="Maroon">i</font> is <a href="xboole_0.html#V1">empty</a>
 <b>by </b><i><a class="ref" href="pboole.html#T24" target="_self">Th24</a>, <a class="ref" href="xboole_1.html#T3">XBOOLE_1:3</a></i>;<br/>


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