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<b>let </b><font color="Maroon">c<sub>1</sub></font> be   <a href="zf_lang.html#NM2">ZF-formula</a>;<br/>

<b>assume </b><a NAME="E1:26"/>
<font color="Maroon">c<sub>1</sub></font> is <a href="zf_lang.html#V10">biconditional</a>
 ;<br/>

<a NAME="E2:26"/><b>then </b>
<font color="Maroon">c<sub>1</sub></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">c<sub>1</sub></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">c<sub>1</sub></font></span>)</span>
 
<b>by </b><i><a class="ref" href="zf_lang.html#T67">ZF_LANG:67</a></i>;<br/>
<a NAME="E3:26"/><b>then </b><i><font color="Green">E10</font></i>: 
<font color="Maroon">c<sub>1</sub></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">c<sub>1</sub></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">c<sub>1</sub></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">c<sub>1</sub></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">c<sub>1</sub></font></span>)</span></span>)</span>
 
;<br/>
<b>hence </b><a NAME="E4:26"/>
<font color="Maroon">c<sub>1</sub></font> is <a href="zf_lang.html#V5">conjunctive</a>
 <b>by </b><i><a class="ref" href="zf_lang.html#T16">ZF_LANG:16</a></i>;<br/>

<a NAME="E5:26"/>
(  <a href="zf_lang.html#K21">the_left_argument_of</a> <font color="Maroon">c<sub>1</sub></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">c<sub>1</sub></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">c<sub>1</sub></font></span>)</span> &amp;  <a href="zf_lang.html#K22">the_right_argument_of</a> <font color="Maroon">c<sub>1</sub></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">c<sub>1</sub></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">c<sub>1</sub></font></span>)</span> )
 
<b>by </b><i><a class="txt" href="zf_lang1.html#E3:26"><i><font color="Green">E10</font></i></a>, <a class="ref" href="zf_lang1.html#T4" target="_self">Th4</a></i>;<br/>
<b>hence </b><a NAME="E6:26"/>
(  <a href="zf_lang.html#K21">the_left_argument_of</a> <font color="Maroon">c<sub>1</sub></font> is <a href="zf_lang.html#V9">conditional</a> &amp;  <a href="zf_lang.html#K22">the_right_argument_of</a> <font color="Maroon">c<sub>1</sub></font> is <a href="zf_lang.html#V9">conditional</a> )
 <b>by </b><i><a class="ref" href="zf_lang.html#T22">ZF_LANG:22</a></i>;<br/>


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