How can I force the argument of a summation to not be offset

Question

Right now, my summation looks like this since I have a long bottom argument:

$\sum\limits_{x \in A[1...i-1]} x$

How can I make it so that the x is not so offset by the bottom argument text?

Answer 1

You could achieve the desired effect by using the \smashoperator macro, which is provided by the mathtools package, with the [r] option. This informs LaTeX that an overlap should be allowed between the material placed below the summation symbol and the material that follows after the summation symbol.

\documentclass{article}
\usepackage{mathtools} % for "\smashoperator" macro
\setlength\textwidth{3in} % just for this example
\begin{document}
No overlap on either side
\[
y = \sum_{x \in A[1,\dots,i-1]} x
\]

\bigskip
Overlap on right-hand side only
\[  % note the option "[r]" in the following line
y = \smashoperator[r]{\sum_{x \in A[1,\dots,i-1]}} x
\]

\bigskip
Overlap on both sides
\[  
y = \smashoperator{\sum_{x \in A[1,\dots,i-1]}} x
\]

\end{document}

Answer 2

See if \mathrlap{...} from mathtools package gives what you like to obtain:

\documentclass[border=3mm,preview]{standalone}
\usepackage{mathtools}

\begin{document}
\[y=\sum\limits_{\mathrlap{x \in A[1...i-1]}} x\]
\end{document}