A D1109: Measurable set $E \in \mathcal{F}$ is an atomic measurable set in $M$ if and only if
(1) | \begin{equation} E \neq \emptyset \end{equation} |
(2) | \begin{equation} \forall \, F \in \mathcal{F} \left( F \subseteq E \quad \implies \quad F = \emptyset \text{ or } F = E \right) \end{equation} |