A relational symbol indicating set membership from right to left, meaning "contains as an element" in set theory.
Examples
Set membership from right to left (reverse ∈)
\mathbb{R} \ni x > 0
Multiple elements in a set
\{x : x \text{ is prime}\} \ni 2, 3, 5, 7
Set builder notation with conditions
\{x \in \mathbb{Z} : -10 \leq x \leq 10\} \ni 0