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<b>let </b><font color="Maroon">L</font> be   <a href="lattices.html#NM2">D_Lattice</a>;<br/><b>let </b><font color="Maroon">b</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">L</font>;<br/><b>let </b><font color="Maroon">a</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">L</font>;<br/>





<b>assume </b><a NAME="E1:32"/><i><font color="Green">E18</font></i>: 
not <font color="Maroon">b</font> <a href="lattices.html#R3">[=</a> <font color="Maroon">a</font>
 ;<br/>

<a NAME="E2:32"/>
<font color="Maroon">b</font> <a href="hidden.html#R2">in</a> <span class="p1"><a href="filter_0.html#K2">&lt;.</a><span class="default"><font color="Maroon">b</font></span><a href="filter_0.html#K2">.)</a></span>
 
;<br/>
<a NAME="E3:32"/><b>then </b><i><font color="Green">E19</font></i>: 
<span class="p1"><a href="filter_0.html#K2">&lt;.</a><span class="default"><font color="Maroon">b</font></span><a href="filter_0.html#K2">.)</a></span> <a href="hidden.html#R2">in</a>  <a href="openlatt.html#K10" target="_self">SF_have</a> <font color="Maroon">b</font>
 
;<br/>
<a NAME="E4:32"/>
not <font color="Maroon">a</font> <a href="hidden.html#R2">in</a> <span class="p1"><a href="filter_0.html#K2">&lt;.</a><span class="default"><font color="Maroon">b</font></span><a href="filter_0.html#K2">.)</a></span>
 
<b>by </b><i>, <a class="ref" href="filter_0.html#T18">FILTER_0:18</a></i>;<br/>
<a NAME="E5:32"/><b>then </b>
not <span class="p1"><a href="filter_0.html#K2">&lt;.</a><span class="default"><font color="Maroon">b</font></span><a href="filter_0.html#K2">.)</a></span> <a href="hidden.html#R2">in</a>  <a href="openlatt.html#K10" target="_self">SF_have</a> <font color="Maroon">a</font>
 
<b>by </b><i><a class="ref" href="openlatt.html#T3" target="_self">Th3</a></i>;<br/>
<b>hence </b><a NAME="E6:32"/>
<span class="p1"><a href="filter_0.html#K2">&lt;.</a><span class="default"><font color="Maroon">b</font></span><a href="filter_0.html#K2">.)</a></span> <a href="hidden.html#R2">in</a> <span class="p1">(<span class="default"><a href="openlatt.html#K10" target="_self">SF_have</a> <font color="Maroon">b</font></span>)</span> <a href="subset_1.html#K7">\</a> <span class="p1">(<span class="default"><a href="openlatt.html#K10" target="_self">SF_have</a> <font color="Maroon">a</font></span>)</span>
 <b>by </b><i>, <a class="ref" href="xboole_0.html#D4">XBOOLE_0:def 4</a></i>;<br/>


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