Block of a set partition
= Block of a set partition
= Blocks of a set partition
{synonym}
A <block of a set partition> is one of its nonempty <subsets>. Distinct <blocks of a set partition> have empty <intersection>, and their <union> is the original <set>. For $\pi=\{\{1,3\},\{2\}\}$, the <blocks of a set partition> are $\{1,3\}$ and the <singleton set> $\{2\}$. The indices in a written list of <blocks of a set partition> do not label or order the <set partition>.