Sections indexed with numbers, subsections with letters

Is it possible to set the environment in such a way that sections are indexed with numbers, and subsections with letters?

I mean, I'd like to have the following result:

1 First section

1.a First subsection

1.b Second subsection

...

2 Second section

2.a First subsection

2.b Second subsection

...

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Redefine \thesubsection as \thesection.\alph{subsection}. (\alph replaces the default \arabic; you could also choose, e.g., \Alph, \roman, and \Roman.)

\documentclass{article}

\renewcommand{\thesubsection}{\thesection.\alph{subsection}}

\begin{document}

\section{First}

\subsection{First-first}

\section{Second}

\end{document}


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