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<b>let </b><font color="Maroon">H</font> be   <a href="zf_lang.html#NM2">ZF-formula</a>;<br/>

<b>assume </b><a NAME="E1:21"/>
<font color="Maroon">H</font> is <a href="zf_lang.html#V10">biconditional</a>
 ;<br/>

<a NAME="E2:21"/><b>then </b>
<font color="Maroon">H</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><a href="zf_lang.html#K27">the_left_side_of</a> <font color="Maroon">H</font></span>)</span> <a href="zf_lang.html#K12">&lt;=&gt;</a> <span class="p1">(<span class="default"><a href="zf_lang.html#K28">the_right_side_of</a> <font color="Maroon">H</font></span>)</span>
 
<b>by </b><i><a class="ref" href="zf_lang.html#T67">ZF_LANG:67</a></i>;<br/>
<a NAME="E3:21"/><b>then </b>
<font color="Maroon">H</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="zf_lang.html#K27">the_left_side_of</a> <font color="Maroon">H</font></span>)</span> <a href="zf_lang.html#K11">=&gt;</a> <span class="p2">(<span class="default"><a href="zf_lang.html#K28">the_right_side_of</a> <font color="Maroon">H</font></span>)</span></span>)</span> <a href="zf_lang.html#K7">'&amp;'</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="zf_lang.html#K28">the_right_side_of</a> <font color="Maroon">H</font></span>)</span> <a href="zf_lang.html#K11">=&gt;</a> <span class="p2">(<span class="default"><a href="zf_lang.html#K27">the_left_side_of</a> <font color="Maroon">H</font></span>)</span></span>)</span>
 
;<br/>
<a NAME="E4:21"/><b>then </b>
(  <a href="zf_lang.html#K21">the_left_argument_of</a> <font color="Maroon">H</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><a href="zf_lang.html#K27">the_left_side_of</a> <font color="Maroon">H</font></span>)</span> <a href="zf_lang.html#K11">=&gt;</a> <span class="p1">(<span class="default"><a href="zf_lang.html#K28">the_right_side_of</a> <font color="Maroon">H</font></span>)</span> &amp;  <a href="zf_lang.html#K22">the_right_argument_of</a> <font color="Maroon">H</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><a href="zf_lang.html#K28">the_right_side_of</a> <font color="Maroon">H</font></span>)</span> <a href="zf_lang.html#K11">=&gt;</a> <span class="p1">(<span class="default"><a href="zf_lang.html#K27">the_left_side_of</a> <font color="Maroon">H</font></span>)</span> )
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E5:21"/>
(  <a href="zf_lang.html#K28">the_right_side_of</a> <font color="Maroon">H</font> <a href="hidden.html#R1">=</a>  <a href="zf_lang.html#K26">the_consequent_of</a> <span class="p1">(<span class="default"><a href="zf_lang.html#K21">the_left_argument_of</a> <font color="Maroon">H</font></span>)</span> &amp;  <a href="zf_lang.html#K28">the_right_side_of</a> <font color="Maroon">H</font> <a href="hidden.html#R1">=</a>  <a href="zf_lang.html#K25">the_antecedent_of</a> <span class="p1">(<span class="default"><a href="zf_lang.html#K22">the_right_argument_of</a> <font color="Maroon">H</font></span>)</span> )
 <b>by </b><i/>;<br/>


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