A D11: Set $X$ is a proper superset of $E$ if and only if
| (1) | $\forall \, x \in E : x \in X$ (D954: Superset) |
| (2) | $E \neq X$ |
| ▼ | Set of symbols |
| ▼ | Alphabet |
| ▼ | Deduction system |
| ▼ | Theory |
| ▼ | Zermelo-Fraenkel set theory |
| ▼ | Set |
| ▼ | Subset |
| ▼ | Superset |
| (1) | $\forall \, x \in E : x \in X$ (D954: Superset) |
| (2) | $E \neq X$ |