# Limits under multiple \sum

I would like to place a lower limit under two consecutive \sums, somewhere in between. So I have \sum_{j=1}^{\infty}\sum_{k=1}^{\infty} and would like to place j>k in the lower limit between the two sums. I believe the multiple integral operator has this kind of functionality.

• Wouldn't \sum_{j=1}^{\infty}\sum_{k=1}^{j} do? – Caramdir Aug 7 '11 at 2:52

Something like:

\mathop{\sum_{j=1}^{\infty}\sum_{k=1}^{\infty}}_{j>k}

maybe?

Looks like this:

Or if you want it on the same line as j=1 and k=1, then maybe:

\mathop{\sum^{\infty}\sum^{\infty}}_{j=1\ j>k\ k=1}

There is an equivalent alternative.

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{mathtools}

\begin{document}
$\underset{j>k}{\sum_{j=1}^{\infty}\sum_{k=1}^{\infty}}$
\end{document}