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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="E1:57"/><i><font color="Green">E45</font></i>: 
<font color="Maroon">c<sub>1</sub></font> is <a href="zf_lang.html#V8" target="_self">disjunctive</a>
 ;<br/>

<a NAME="E2:57"/><b>then </b>
ex <font color="Olive">b<sub>1</sub></font> being  <a href="zf_lang.html#NM2">ZF-formula</a> st <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#K21" target="_self">the_left_argument_of</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="zf_lang.html#K10" target="_self">'or'</a> <font color="Olive">b<sub>1</sub></font>
 
<b>by </b><i><a class="ref" href="zf_lang.html#T57" target="_self">Th57</a></i>;<br/>
<b>hence </b><a NAME="E3:57"/>
<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#K21" target="_self">the_left_argument_of</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="zf_lang.html#K10" target="_self">'or'</a> <span class="p1">(<span class="default"><a href="zf_lang.html#K22" target="_self">the_right_argument_of</a> <font color="Maroon">c<sub>1</sub></font></span>)</span>
 <b>by </b><i><a class="txt" href="zf_lang.html#E1:57"><i><font color="Green">E45</font></i></a>, <a class="ref" href="zf_lang.html#T57" target="_self">Th57</a></i>;<br/>


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