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<b>let </b><font color="Maroon">n</font> be  <a href="ordinal1.html#V7">natural</a>  <a href="ordinal1.html#NM1" target="_self">number</a> ;<br/>

<a NAME="E1:18"/>
 <a href="catalan1.html#K1" target="_self">Catalan</a> <font color="Maroon">n</font> is   <a href="int_1.html#NM1">Integer</a>
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E2:18"/>
 <a href="catalan1.html#K1" target="_self">Catalan</a> <font color="Maroon">n</font> is    <a href="subset_1.html#M1">Element</a> of  <a href="numbers.html#K5">NAT</a> 
 <b>by </b><i><a class="ref" href="int_1.html#T16">INT_1:16</a></i>;<br/>


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