1

I have the following situation:

\documentclass[fleqn]{article}
\usepackage{amsmath}
\usepackage{mathtools}
\begin{document}
  \begin{gather*}
  [a,b]=c, \\
  [c,d]=f, \\
  \left.
  \begin{lgathered}
  [a,b]=c, \\
  [c,d]=f, 
  \end{lgathered}
  \right\} \text{some annotation} \\
  [a,b]=c, \\
  [c,d]=f, 
  \end{gather*}
\end{document}

which results in the maddening enter image description here

We have to cancel the extra space before the *ed environment, but also the one that gets put because of the left delimiter, and I don't seem to be able to get it right. Is there a sane way to do this correctly?

1

2 Answers 2

4

The space from \left. is \nulldelimiterspace so you can set that to 0pt or as here just correct by that amount.

lgathered adds a \, before alignment, copying an old bug in gathered that was fixed last year. The package probably should be updated to match amsmath but you can use \! in the meantime so

\documentclass[fleqn]{article}

\usepackage{mathtools}
\begin{document}
  \begin{gather*}
  [a,b]=c, \\
  [c,d]=f, \\
  \kern-\nulldelimiterspace\left.\!
  \begin{lgathered}
  [a,b]=c, \\
  [c,d]=f, 
  \end{lgathered}
  \right\} \text{some annotation} \\
  [a,b]=c, \\
  [c,d]=f, 
  \end{gather*}
\end{document}
1
  • 1
    Updated mathtools (about the \,) has just been sent off to CTAN.
    – daleif
    Oct 30, 2017 at 11:41
2

You can add some negative math kerning before the \gathered environment. I would suggest using the rcases instead to simplify the code + some (less) negative math kerning. Also, note you don't have to load amsmath since mathtools does it for you:

\documentclass[fleqn]{article}
\usepackage{mathtools}

\begin{document}

  \begin{gather*}
  [a,b]=c, \\
  [c,d]=f, \\
  \mkern -2.2mu
  \begin{rcases}
  [a,b]=c, \\
  [c,d]=f,
  \end{rcases}
   \text{some annotation} \\
  [a,b]=c, \\
  [c,d]=f,
  \end{gather*}

\end{document} 

enter image description here

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