[Tex/LaTex] How to reduce spacing in aligned equations

Question

I currently have the following markup to render aligned equations:

\[
\begin{split}
\sum_{j=1}^{n+1} j \cdot j! &= \overbrace{(n+1)!-1}^{A(n)} + (n+1) \cdot (n+1)! \\
&= ((n+1)+1) \cdot (n+1)! - 1 \\
&= (n+2) \cdot (n+1)! - 1 \\
&= (n+2)!-1
\end{split}
\]

It seems like the summation is creating an awkward non-uniform space between the first and second lines:

I understand why it's happening, but is there a way to prevent this from happening and reduce the spacing between the first and second lines?

Answer 1

We can use \smash to get rid of the excess space completely, and it doesn't involve any tweaking of lengths by eye.

The result may or may not be to your taste though.

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\[
  \begin{split}
    \smash{\sum_{j=1}^{n+1}} j \cdot j! &= \overbrace{(n+1)!-1}^{A(n)} + (n+1) \cdot
    (n+1)! \\
    &= ((n+1)+1) \cdot (n+1)! - 1 \\
    &= (n+2) \cdot (n+1)! - 1 \\
    &= (n+2)!-1
  \end{split}
\]

\end{document}