\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  [ \Delta_1, \Delta_{i-1}] = \mbox{span} \{ [g,h]: g \in \Delta_1, h
\in \Delta_{i-1} \}.
\end{equation*}
\end{document}