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<b>let </b><font color="Maroon" title="c1">H</font> be   <a href="zf_lang.html#NM2" title="ZF_LANG:NM.2">ZF-formula</a>;<br/><b>let </b><font color="Maroon" title="c2">x</font>, <font color="Maroon" title="c3">y</font> be   <a href="zf_lang.html#NM1" title="ZF_LANG:NM.1">Variable</a>;<br/>





<b>given </b><font color="Maroon" title="c4">H1</font>, <font color="Maroon" title="c5">H2</font> being   <a href="zf_lang.html#NM2" title="ZF_LANG:NM.2">ZF-formula</a><b> such that </b><a NAME="E2:175"/><i><font color="Green" title="E75">A1</font></i>: 
<font color="Maroon" title="c1">H</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c4">H1</font> <a href="zf_lang.html#K12" title="ZF_LANG:func.12">&lt;=&gt;</a> <font color="Maroon" title="c5">H2</font>
 ; <i><font color="Red">:: according to </font></i><a class="ref" href="zf_lang.html#D22" title="ZF_LANG:def.22">ZF_LANG:def 22</a><br/>

<a NAME="E3:175"/>
<font color="Maroon" title="c1">H</font> <a href="zf_lang1.html#K6" title="ZF_LANG1:func.6">/</a> <font color="Maroon" title="c2">x</font>,<font color="Maroon" title="c3">y</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <span class="p1">(<span class="default"><font color="Maroon" title="c4">H1</font> <a href="zf_lang1.html#K6" title="ZF_LANG1:func.6">/</a> <font color="Maroon" title="c2">x</font>,<font color="Maroon" title="c3">y</font></span>)</span> <a href="zf_lang.html#K12" title="ZF_LANG:func.12">&lt;=&gt;</a> <span class="p1">(<span class="default"><font color="Maroon" title="c5">H2</font> <a href="zf_lang1.html#K6" title="ZF_LANG1:func.6">/</a> <font color="Maroon" title="c2">x</font>,<font color="Maroon" title="c3">y</font></span>)</span>
 
<b>by </b><i><a class="txt" href="zf_lang1.html#E2:175"><i><font color="Green" title="E75">A1</font></i></a>, <a class="ref" href="zf_lang1.html#T177" target="_self" title="ZF_LANG1:th.177">Th177</a></i>;<br/>
<b>hence </b><a NAME="E4:175"/>
<font color="Maroon" title="c1">H</font> <a href="zf_lang1.html#K6" title="ZF_LANG1:func.6">/</a> <font color="Maroon" title="c2">x</font>,<font color="Maroon" title="c3">y</font> is <a href="zf_lang.html#V10" title="ZF_LANG:attr.10">biconditional</a>
 <b>by </b><i><a class="ref" href="zf_lang.html#T22" title="ZF_LANG:th.22">ZF_LANG:22</a></i>;<br/>


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