Double brackets {{ }} [duplicate]

Question

How to type the double bracket '{{b, a}}' in tex just as the picture below?

Answer 1

You need negative spaces \! to get the braces close to each other. There may be a better way.

\documentclass{article}

\begin{document}

\( \{\!\!\{a,b\}\!\!\} \)

\end{document}

Answer 2

\documentclass{article}

\newcommand\doubleBrackets[1]{$\{\!\{ #1 \}\!\}$}

\begin{document}

These are double \{ \} brackets \doubleBrackets{b, a}.

\end{document}