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<b>let </b><font color="Maroon">L</font> be   <a href="lattices.html#NM1">Lattice</a>;<br/><b>let </b><font color="Maroon">D1</font> be  non <a href="xboole_0.html#V1">empty</a> <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">L</font>;<br/><b>let </b><font color="Maroon">D2</font> be  non <a href="xboole_0.html#V1">empty</a> <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">L</font>;<br/>





<b>assume </b><a NAME="E1:28"/><i><font color="Green">E28</font></i>: 
<font color="Maroon">D1</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">D2</font>
 ;<br/>

<a NAME="E2:28"/>
<font color="Maroon">D2</font> <a href="tarski.html#R1">c=</a> <span class="p1"><a href="filter_0.html#K3" target="_self">&lt;.</a><span class="default"><font color="Maroon">D2</font></span><a href="filter_0.html#K3" target="_self">.)</a></span>
 
<b>by </b><i/>;<br/>
<a NAME="E3:28"/><b>then </b>
<font color="Maroon">D1</font> <a href="tarski.html#R1">c=</a> <span class="p1"><a href="filter_0.html#K3" target="_self">&lt;.</a><span class="default"><font color="Maroon">D2</font></span><a href="filter_0.html#K3" target="_self">.)</a></span>
 
<b>by </b><i>, <a class="ref" href="xboole_1.html#T1">XBOOLE_1:1</a></i>;<br/>
<b>hence </b><a NAME="E4:28"/>
<span class="p1"><a href="filter_0.html#K3" target="_self">&lt;.</a><span class="default"><font color="Maroon">D1</font></span><a href="filter_0.html#K3" target="_self">.)</a></span> <a href="tarski.html#R1">c=</a> <span class="p1"><a href="filter_0.html#K3" target="_self">&lt;.</a><span class="default"><font color="Maroon">D2</font></span><a href="filter_0.html#K3" target="_self">.)</a></span>
 <b>by </b><i/>;<br/>


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