Question

I am looking for a way to typeset two variables over each other similar to binom{n}{k} or {n choose k}. The only difference is that it should be surrounded in curly braces instead of round ones. Is there a proper way to do it?

My workaround

I've already attempted working around this using the following approach:

documentclass{article}



usepackage{amsmath}

usepackage{mathtools}

begin{document}

    This is a text containing

    $begin{cases}

        begin{rcases}

            n \

            k\

        end{rcases}

    end{cases}$,

    my mathematical symbol.



    My binomial $binom{n}{k}$ for comparison.

end{document}

Unfortunately, it is an ugly workaround. The braces and size of the font are too big, as seen compared to the properly typeset binomial. Additionally, there's a huge amount of space on the right.

You should construct it the same way amsmath's binom uses genfrac{<ldelim>}{<rdelim>}{<width>}{<math style>}{<numerator>}{<denominator>}:

documentclass{article}



usepackage{amsmath}



newcommand{bracenom}{genfrac{lbrace}{rbrace}{0pt}{}}



begin{document}



My binomial $binom{n}{k}$ for comparison with $bracenom{n}{k}$.



end{document}

Leaving the <math style> empty implies that the current math style will be used. You can also define dbracenom to use <math style> = 0 and tbracenom to use <math style> = 1. Here are the similar definitions for binom-and-friends:

DeclareRobustCommand{binom}{genfrac()z@{}}

newcommand{dbinom}{genfrac(){0pt}0}

newcommand{tbinom}{genfrac(){0pt}1}

<width> refers to the rule between the <numerator> and <denominator>.