\longmapstoThe \longmapsto command in LaTeX is used to produce a long arrow with a mapsto symbol, typically used in mathematical functions to denote mapping from one set to another.
Function mapping x to x squared
f : x \longmapsto x^2Mapping from group G to group H
\varphi : G \longmapsto HMapping each element x to x plus one
x \longmapsto x + 1