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<b>let </b><font color="Maroon">T</font> be  non <a href="struct_0.html#V3">empty</a>  <a href="struct_0.html#L1">1-sorted</a> ;<br/><b>let </b><font color="Maroon">N</font> be  non <a href="struct_0.html#V3">empty</a>  <a href="waybel_0.html#L1">NetStr</a> of <font color="Maroon">T</font>;<br/><b>let </b><font color="Maroon">B</font> be    <a href="hidden.html#M1">set</a> ;<br/>





<a NAME="E1:13"/>
( <font color="Maroon">B</font> <a href="hidden.html#R2">in</a>  <a href="yellow19.html#K2" target="_self">a_filter</a> <font color="Maroon">N</font> iff  ex <font color="Olive">A</font> being  <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font> st <br/>( <font color="Maroon">B</font> <a href="hidden.html#R1">=</a> <font color="Olive">A</font> &amp; <font color="Maroon">N</font> <a href="waybel_0.html#R1">is_eventually_in</a> <font color="Olive">A</font> ) )
 
;<br/>
<b>hence </b><a NAME="E2:13"/>
( <font color="Maroon">B</font> <a href="hidden.html#R2">in</a>  <a href="yellow19.html#K2" target="_self">a_filter</a> <font color="Maroon">N</font> iff ( <font color="Maroon">N</font> <a href="waybel_0.html#R1">is_eventually_in</a> <font color="Maroon">B</font> &amp; <font color="Maroon">B</font> is   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font> ) )
 ;<br/>


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