How to make the subindex appear below the arrow?

Question

I want to write a limit with the "arrows' notation." This is, instead of \lim_{n \rightarrow \infty} x_{n} = x I want to use x_{n} \rightarrow_{n \rightarrow \infty} x. My problem is that with this last code, the n \rightarrow \infty appears down to the right of the arrow, and I would like it to appear below the arrow. How can I do that?

Answer 1

You can use the extensible arrow \xrightarrow provided by amsmath, which has two arguments, an optional one for text below the arrow and a mandatory one for text above the arrow

\xrightarrow[text below]{text above}

In your case you have to use

\xrightarrow[n \to \infty]{}

MWE

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\[
x_{n} \xrightarrow[n \to \infty]{} x
\]

\end{document} 

Note that in the limit it's better to use \to rather than \rightarrow

Answer 2

Here's a way with the amsmath package's \underset macro.

\documentclass{article}
\usepackage{amsmath}
\def\xtend{-\!\!\!}
\begin{document}
\[ x_{n} \underset{\scriptscriptstyle n \rightarrow \infty}{\xtend\xtend\rightarrow} x\]
\end{document}

Here's a way with a stack. the option argument (here [2pt]) controls the depth of the underset.

\documentclass{article}
\usepackage{stackengine}
\stackMath
\def\xtend{-\!\!\!}
\begin{document}
\[ x_{n} \mathrel{%
  \stackunder[2pt]{\xtend\xtend\rightarrow}{\scriptscriptstyle n \rightarrow \infty}} x\]
\end{document}