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<b>let </b><font color="Maroon" title="c1">x</font> be   <a href="qc_lang1.html#NM3" title="QC_LANG1:NM.3">bound_QC-variable</a>;<br/><b>let </b><font color="Maroon" title="c2">r</font> be    <a href="subset_1.html#M2" title="SUBSET_1:mode.2">Element</a> of  <a href="cqc_lang.html#K7" title="CQC_LANG:func.7">CQC-WFF</a> ;<br/>



<a NAME="E1:58"/>
 <a href="qc_lang3.html#K5" title="QC_LANG3:func.5">Free</a> <font color="Maroon" title="c2">r</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a>  <a href="xboole_0.html#K1" title="XBOOLE_0:func.1">{}</a> 
 
<b>by </b><i><a class="ref" href="cqc_lang.html#T13" target="_self" title="CQC_LANG:th.13">Th13</a></i>;<br/>
<b>hence </b><a NAME="E2:58"/>
<font color="Maroon" title="c2">r</font> <a href="cqc_lang.html#K17" title="CQC_LANG:func.17">.</a> <font color="Maroon" title="c1">x</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c2">r</font>
 <b>by </b><i><a class="ref" href="cqc_lang.html#T39" target="_self" title="CQC_LANG:th.39">Th39</a></i>;<br/>


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