(i) | $E \subseteq X$ is a D78: Subset of $X$ |

**subnull set**in $M$ if and only if there exists D1109: Measurable set $F \in \mathcal{F}$ such that

(1) | \begin{equation} E \subseteq F \end{equation} | (D78: Subset) |

(2) | \begin{equation} \mu(F) = 0 \end{equation} | (D1676: Null measurable set) |