In mathematics, the arrow $\mapsto$ (which in LaTeX is called "\mapsto") is used to describe what a function does to an arbitrary input. It is commonly used in combination with colon-to notation, which describes what a function's domain and codomain are.

By itself, $\mapsto$ can be used to describe a function without naming it, and so is a way to describe anonymous functions in mathematics.

Examples

The function $f\left(x\right)=x^2$ from the real numbers to the real numbers can be described using a combination of colon-to notation and mapsto notation as

$$f:R\to R$$ $$x\mapsto x^2.$$

In one line, although this is less common,

$$f:R\ni x\mapsto x^2\in R.$$

(see in notation).