Definition:Atom of Sigma-Algebra

Definition
Let $X$ be a set, and let $\mathcal A$ be a $\sigma$-algebra on $X$.

Let $A \in \mathcal A$ be nonempty.

$A$ is said to be an atom (of $\mathcal A$) iff it satisfies:


 * $\forall B \in \mathcal A: B \subsetneq A \implies B = \varnothing$