\input{umtest-preamble} \usepackage{amsmath} \usepackage{unicode-math} \setmathfont{Cambria Math} \begin{document} \[ \sum_{\substack{a \\ bbb}} \sum_{\substack{\dfrac12 \\ \vec A'}} \sum_{\begin{subarray}{l} a \\ bbb \end{subarray}} \] \end{document}