Let $E_j$ be a D11: Set for each $j \in J$.
Then
| (1) | \begin{equation} \bigcap_{j \in J} E_j \subseteq \bigcup_{j \in J} E_j \end{equation} |
| (2) | \begin{equation} \bigcap_{j \in J} E_j = \bigcup_{j \in J} E_j \quad \iff \quad \forall \, j \in J \, ( E_j = E ) \end{equation} |