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<b>let </b><font color="Maroon">D</font> be  non <a href="xboole_0.html#V1">empty</a>  <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">p</font> be    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">D</font>;<br/><b>let </b><font color="Maroon">f</font> be    <a href="finseq_1.html#M2">FinSequence</a> of <font color="Maroon">D</font>;<br/>





<b>assume </b><a NAME="E1:68"/>
<font color="Maroon">p</font> <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K2">rng</a> <font color="Maroon">f</font>
 ;<br/>

<a NAME="E2:68"/><b>then </b>
 ex <font color="Olive">i</font> being   <a href="subset_1.html#M1">Element</a> of  <a href="numbers.html#K5">NAT</a>  st <br/>( <font color="Olive">i</font> <a href="nat_1.html#K1">+</a> 1 <a href="hidden.html#R1">=</a> <font color="Maroon">p</font> <a href="finseq_4.html#K5">..</a> <font color="Maroon">f</font> &amp; <font color="Maroon">f</font> <a href="finseq_5.html#K2" target="_self">:-</a> <font color="Maroon">p</font> <a href="hidden.html#R1">=</a> <font color="Maroon">f</font> <a href="rfinseq.html#K1">/^</a> <font color="Olive">i</font> )
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E3:68"/>
(  not <font color="Maroon">f</font> is <a href="funct_1.html#V2">one-to-one</a> or <font color="Maroon">f</font> <a href="finseq_5.html#K2" target="_self">:-</a> <font color="Maroon">p</font> is <a href="funct_1.html#V2">one-to-one</a> )
 <b>by </b><i/>;<br/>


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