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<p>The lattice of noncrossing partitions of a finite set forms a subset of the lattice of all partitions, but not a sublattice, since the join operations of the two lattices do not agree.</p>

<p>The noncrossing partition lattice has taken on importance because of its role in <a href="page.php?w=free_probability">free probability</a> theory.</p>

<p><big> Counting partitions </big></p>
<p>The total number of partitions of an n-element set is the <a href="page.php?w=Bell_numbers">Bell number</a> B<sub>n</sub>. The first several Bell numbers are B<sub>0</sub> =</p><p>
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