parentheses vs brackets for indexed family of sets I understand the definition of parentheses and brackets. However this problem involving indexed family of sets has me questioning the definitions.
Q: Let $\mathscr A = \{[-x,0]: x \in \mathbb R \text{ and } 0 < x < 1\}$.
Find the union over $\mathscr A$ and the intersection over $\mathscr A.$
$(-1,0]$ is correct.
The number $-1$ is not an element of any set in the family $\mathcal{A}$ and therefore cannot be in the union.
