$$
\displaystyle {\displaystyle{a\over b}\brace \displaystyle{c\over d}}
\textstyle {\displaystyle{a\over b}\brace \displaystyle{c\over d}}
\scriptstyle {\displaystyle{a\over b}\brace \displaystyle{c\over d}}
\scriptscriptstyle {\displaystyle{a\over b}\brace \displaystyle{c\over d}}
$$
