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<b>let </b><font color="Maroon" title="c1">p</font>, <font color="Maroon" title="c2">q</font> be   <a href="zf_lang.html#NM2" title="ZF_LANG:NM.2">ZF-formula</a>; <a class="txt" onclick="hs(this)" href="javascript:()"><i><font color="Red">::  thesis: </font></i></a><span class="hide"> (  <a href="zf_lang.html#K27" title="ZF_LANG:func.27">the_left_side_of</a> <span class="p1">(<span class="default"><font color="Maroon" title="c1">p</font> <a href="zf_lang.html#K12" title="ZF_LANG:func.12">&lt;=&gt;</a> <font color="Maroon" title="c2">q</font></span>)</span> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c1">p</font> &amp;  <a href="zf_lang.html#K28" title="ZF_LANG:func.28">the_right_side_of</a> <span class="p1">(<span class="default"><font color="Maroon" title="c1">p</font> <a href="zf_lang.html#K12" title="ZF_LANG:func.12">&lt;=&gt;</a> <font color="Maroon" title="c2">q</font></span>)</span> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c2">q</font> )</span><br/>



<a NAME="E1:7"/>
<font color="Maroon" title="c1">p</font> <a href="zf_lang.html#K12" title="ZF_LANG:func.12">&lt;=&gt;</a> <font color="Maroon" title="c2">q</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/>
<a NAME="E2:7"/><b>then </b>
<font color="Maroon" title="c1">p</font> <a href="zf_lang.html#K12" title="ZF_LANG:func.12">&lt;=&gt;</a> <font color="Maroon" title="c2">q</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <span class="p1">(<span class="default"><a href="zf_lang.html#K27" title="ZF_LANG:func.27">the_left_side_of</a> <span class="p2">(<span class="default"><font color="Maroon" title="c1">p</font> <a href="zf_lang.html#K12" title="ZF_LANG:func.12">&lt;=&gt;</a> <font color="Maroon" title="c2">q</font></span>)</span></span>)</span> <a href="zf_lang.html#K12" title="ZF_LANG:func.12">&lt;=&gt;</a> <span class="p1">(<span class="default"><a href="zf_lang.html#K28" title="ZF_LANG:func.28">the_right_side_of</a> <span class="p2">(<span class="default"><font color="Maroon" title="c1">p</font> <a href="zf_lang.html#K12" title="ZF_LANG:func.12">&lt;=&gt;</a> <font color="Maroon" title="c2">q</font></span>)</span></span>)</span>
 
<b>by </b><i><a class="ref" href="zf_lang.html#T67" title="ZF_LANG:th.67">ZF_LANG:67</a></i>;<br/>
<b>hence </b><a NAME="E3:7"/>
(  <a href="zf_lang.html#K27" title="ZF_LANG:func.27">the_left_side_of</a> <span class="p1">(<span class="default"><font color="Maroon" title="c1">p</font> <a href="zf_lang.html#K12" title="ZF_LANG:func.12">&lt;=&gt;</a> <font color="Maroon" title="c2">q</font></span>)</span> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c1">p</font> &amp;  <a href="zf_lang.html#K28" title="ZF_LANG:func.28">the_right_side_of</a> <span class="p1">(<span class="default"><font color="Maroon" title="c1">p</font> <a href="zf_lang.html#K12" title="ZF_LANG:func.12">&lt;=&gt;</a> <font color="Maroon" title="c2">q</font></span>)</span> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c2">q</font> )
 <b>by </b><i><a class="ref" href="zf_lang.html#T50" title="ZF_LANG:th.50">ZF_LANG:50</a></i>; <a class="txt" onclick="hs(this)" href="javascript:()"><i><font color="Red">::  thesis: </font></i></a><span class="hide"> verum</span><br/>


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