\documentclass{report}

\ifx\bmatrix\UNDEFINED\usepackage{amsmath}\fi
\thispagestyle{empty}
\begin{document}
\begin{displaymath}
\left[0,\#x\mathit{D7FF}\right] \cup \left[\#x\mathit{E000}, \#x\mathit{10FFFF}\right]
\end{displaymath}
\end{document}
