5

Using the definition theorem style from amsthm does not enable the reader to separate between text that belongs to the definition and the text following it. Example:

\documentclass{scrbook}
\usepackage{amsthm}
\theoremstyle{definition}
\newtheorem{defi}{Definition}

\begin{document}

  \begin{defi}
    Some Definition.
  \end{defi}

  Some text.
\end{document}

Do you have any advice how to make the border between some definition and the following text more clear? Are there any standard solutions which look professional at the same time? What is your experience?

I could think of different solutions:

  1. Adding something like the \qed symbol at the end of each definition. But in my view q.e.d would be semantically wrong in this context.
  2. Changing the font in any way, e.g. making it italic like in the theorem environment. On the other hand, this would make the definition style useless...
  3. Adding some extra space. I don't like this solution...
4
  • You can use another "qed" symbol for definitions e.g. a small black square, or a diamond. Don't know whether this is possible with amsthm, though. It's possible with ntheorem — which is better at placing automatically qed symbols when a proof ends with a display equation.
    – Bernard
    Mar 24, 2014 at 17:07
  • They are separated by a vertical space.
    – egreg
    Mar 24, 2014 at 17:29
  • You can also separate the definition using framing environments from tcolorbox or mdframed. If a full frame seems to offensive, both packages would allow doing less flashy effects like e.g. a simple vertical rule following the text. The documentations of these packages offer many examples. Mar 24, 2014 at 18:17
  • looks like in 2016 there has been a similar question with more responses: tex.stackexchange.com/questions/291346/…
    – matheburg
    Mar 21, 2023 at 3:21

1 Answer 1

1

The visual separation is already provided by the vertical space before and after the environment. The fact it is a definition stands out also because of the missing indentation before “Definition” and the different weight/shape of the character used.

This is a reason for not using spaced paragraphs, which make it difficult to distinguish between different parts.

There's no need for other visual clues.

Example:

\documentclass{article}
\usepackage{amsthm}
\usepackage{lipsum}

\theoremstyle{definition}
\newtheorem{defi}{Definition}

\begin{document}

\lipsum[1]

\begin{defi}
A group $G$ is called \emph{abelian} if, for all $a,b\in G$, $ab=ba$ or,
in other words, the operation on $G$ is commutative.
\end{defi}

\lipsum[3]

\end{document}

enter image description here

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  • Thank you, I agree with you argumentation. Nevertheless, adding some more paragraphs in and outside the definition doesn't make it as clear as in your example anymore. Especially if you have a slightly increased parskip.
    – matheburg
    Mar 25, 2014 at 6:58

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