With the amsmath packages, you can define anything to appear like a "large operator", so that superscripts are written on top, and subscripts below, using the \mathop{...} command. Consider, e.g.:
Code: Select all
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
\mathop{\Bigg[}_a^b
\]
\end{document}
(Use a different size command than \Bigg if need be.)
If it were me I'd define a new command for using this, but I suppose if you wanted to replace the integral sign, you could use
\renewcommand{\int}{\mathop{\Bigg[}}