A longer arrow symbol indicating function mappings or transformations between mathematical spaces in category theory.
Examples
Function definition with explicit mapping
x \longmapsto x^2 + 1
Named function with domain and codomain
f: \mathbb{R} \ni x \longmapsto ax + b \in \mathbb{R}
Explicit set mapping
\{1,2,3\} \ni n \longmapsto 2n \in \{2,4,6\}