Partition atom
= Partition atom
{title2=$A\in\xi$}
A partition atom is a member of a <measurable partition>. For a finite or countable partition, each cell is an <atom of a sigma-algebra> generated by that partition, whose measurable sets are unions of cells. A partition atom need not be an <atom of a measure>: an interval cell with positive <Lebesgue measure> can be split into smaller positive-measure sets that lie outside the generated partition sigma-algebra.