[Tex/LaTex] How to build two lines aligned maps

Question

I would like to write a map between two objects, with a map below which specify where any single object is sent. To be more precise. I want to write $A \rightarrow B$, and right below it $\alpha \mapsto \beta$. I tried with the command $\underset$ but the maps below gets too smaller, and it's not aligned to the map above. What is the right command?

I apologize if this question has been already asked. To me it looks elementary, nevertheless I couldn't find it nor here nor googling around. Thank you very much for your time!

Answer 1

Something like this or variants like aligned if you want it to be part of a larger expression.

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align*}
A&\rightarrow B\\
a&\mapsto b
\end{align*}

\end{document}