Nested expressions in equations

Question

Is it possible to type something like this (in math mode):

A = B

and put something below the = sign (such as x\rightarrow\something)?

Answer 1

You can use \underset from the amsmath package:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

$A\underset{x\to a}{=} B$

\end{document}

I am not sure if I understood your intent correctly, though.