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<b>let </b><font color="Maroon" title="c1">X</font> be    <a href="hidden.html#M1" title="HIDDEN:mode.1">set</a> ;<br/><b>let </b><font color="Maroon" title="c2">F</font> be   <a href="armstrng.html#NM2" title="ARMSTRNG:NM.2">Dependency-set</a> of <font color="Maroon" title="c1">X</font>;<br/>



<b>assume </b><a NAME="E1:63"/>
( <font color="Maroon" title="c2">F</font> is <a href="armstrng.html#V3" title="ARMSTRNG:attr.3">(F1)</a> &amp; <font color="Maroon" title="c2">F</font> is <a href="armstrng.html#V4" title="ARMSTRNG:attr.4">(F3)</a> )
 ;<br/>

<b>then reconsider </b><font color="Maroon" title="c3">F'</font> = <font color="Maroon" title="c2">F</font> as  <a href="armstrng.html#V3" title="ARMSTRNG:attr.3">(F1)</a> <a href="armstrng.html#V4" title="ARMSTRNG:attr.4">(F3)</a> <a href="armstrng.html#NM2" title="ARMSTRNG:NM.2">Dependency-set</a> of <font color="Maroon" title="c1">X</font> ;<br/>
<a NAME="E3:63"/>
<font color="Maroon" title="c3">F'</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c2">F</font>
 
;<br/>
<b>hence </b><a NAME="E4:63"/>
<font color="Maroon" title="c2">F</font> is <a href="armstrng.html#V7" title="ARMSTRNG:attr.7">(DC3)</a>
 ;<br/>


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