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<a NAME="E1:17_2_1"/>
<font color="Maroon">x</font> <a href="zf_lang.html#K5" target="_self">'in'</a> <font color="Maroon">y</font> is <a href="zf_lang.html#V1" target="_self">ZF-formula-like</a>
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="17_2_1_1"><b>proof </b></a><div class="add">

<b>thus </b><a NAME="E1:17_2_1_1"/>
<font color="Maroon">x</font> <a href="zf_lang.html#K5" target="_self">'in'</a> <font color="Maroon">y</font> is    <a href="subset_1.html#M1">Element</a> of  <a href="zf_lang.html#K9" target="_self">WFF</a> 
 <b>by </b><i/>; <i><font color="Red">:: according to </font></i><a class="ref" href="zf_lang.html#D9" target="_self">ZF_LANG:def 9</a><br/>


</div><b>end;</b></div>
<b>hence </b><a NAME="E2:17_2_1"/>
<font color="Maroon">x</font> <a href="zf_lang.html#K5" target="_self">'in'</a> <font color="Maroon">y</font> is <a href="zf_lang.html#V1" target="_self">ZF-formula-like</a>
 ;<br/>


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