[Tex/LaTex] Alternative theorem styles with amsthm package

amsthm

I am writing a document with many lemmas, theorems, and proofs. I don't like the default styling available, mainly because it places almost no visual separation between theorems and text (or proofs and text).

I would like the following:

A definiton environment with larger margins and a vertical line on the left side, so I can clearly see where the definition starts and ends, by noticing where the vertical line begins and ends.

Is there any theorem style that would achieve this? Any similar style which would at least make the theorems and proofs stand out from the text?

Thanks!

p.s. Currently, I end a definition block with a \( \qed \) so there is some indication that the definition ended.

Best Answer

You can use mdframed:

\documentclass{article}
\usepackage{amsthm}
\usepackage[framemethod=tikz]{mdframed}
\usepackage{lipsum}

\theoremstyle{plain}
\newmdtheoremenv[
  linecolor=cyan,
  roundcorner=5pt,
  linewidth=1pt
]{theo}{Theorem}

\theoremstyle{definition}
\newmdtheoremenv[
  hidealllines=true,
  leftline=true,
  innerleftmargin=10pt,
  innerrightmargin=10pt,
  innertopmargin=0pt,
]{defi}{Definition}

\begin{document}

\lipsum[4]
\begin{defi}
\lipsum[4]
\end{defi}
\lipsum[4]
\begin{theo}
\lipsum[4]
\end{theo}

\end{document}

enter image description here

The package offers many additional customization options; please refer to the package documentation which also contains numerous examples.

If a same style is to be used for several structures, then it's better to define a style to be used multiple times; the package also offers a very useful \surroundwithmdframed command to apply mdframed settings to an already defined environment. In the following example I define a style, built an structure for definitions using this style, and surround the standard proof environment (from amsthm) with this style:

\documentclass{article}
\usepackage{amsthm}
\usepackage[framemethod=tikz]{mdframed}
\usepackage{lipsum}

\mdfdefinestyle{mystyle}{
  hidealllines=true,
  leftline=true,
  innerleftmargin=10pt,
  innerrightmargin=10pt,
  innertopmargin=0pt,
}
\surroundwithmdframed[style=mystyle]{proof}
\theoremstyle{definition}
\newmdtheoremenv[style=mystyle]{defi}{Definition}

\begin{document}

\lipsum[4]
\begin{defi}
\lipsum[4]
\end{defi}
\lipsum[4]
\begin{proof}
\lipsum*[4]
\end{proof}

\end{document}

enter image description here

Related Solutions

[Tex/LaTex] amsthm: how to reduce the vertical spacing between theorem and proof

One possibility would be to redefine the proof anvironment as defined in amsthm.sty (the definition uses \topsep6\p@\@plus6\p@\relax, so you could make some changes there). Another approach would be to use the front-end thmtools to define a new theorem-like structure behaving like the standard proof environment, but using the spaceabove key to control the vertical space above it. The following example illustrates this second approach and shows the different spacing for the new prf environment and the standard proof environment:

\documentclass{article} 
\usepackage{amsthm} 
\usepackage{thmtools}

\declaretheorem{theorem} 
\declaretheoremstyle[%
  spaceabove=-6pt,%
  spacebelow=6pt,%
  headfont=\normalfont\itshape,%
  postheadspace=1em,%
  qed=\qedsymbol%
]{mystyle} 
\declaretheorem[name={Proof},style=mystyle,unnumbered,
]{prf}

\begin{document} 

\begin{theorem} 
A really important result.
\end{theorem}
\begin{prf} 
And its proof with less space above.
\end{prf} 
\begin{theorem} 
A really important result.
\end{theorem}
\begin{proof} 
And its proof with too much space above.
\end{proof} 

\end{document}

enter image description here

[Tex/LaTex] Indicator at end of theorem

You can use the QED mechanism that amsthm provides: define an appropriate symbol, push a QED at the beginning of the theorem, pop it at the end. You can then put \qedhere somewhere if you need the marker earlier, and the final pop will then do nothing.

Sample output

\documentclass{book}
\usepackage{amsthm}
\parindent0pt

\newcommand{\thmsymbol}{\( \diamond \)}

\theoremstyle{definition}
\newtheorem{theorem}{Theorem}

\newenvironment{thm}{\begin{theorem}%
  \renewcommand{\qedsymbol}{\thmsymbol}\pushQED{\qed}}%
  {\popQED\end{theorem}}

\begin{document}

\begin{thm}
  This is some long theorem. Lorem ipsum dolor sit amet, consetetur
  sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore
  et dolore magna aliquyam erat, sed diam voluptua. At vero eos et
  accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren,
  no sea takimata sanctus est Lorem ipsum dolor sit amet.
  \begin{enumerate}
  \item Part A
  \item Part B
  \end{enumerate}

  Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam
  nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam
  erat, sed diam voluptua. At vero eos et accusam et justo duo dolores
  et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est
  Lorem ipsum dolor sit amet.
\end{thm}

Here is some text not in the theorem anymore.

\begin{thm}
  Here is some other theorem that ends with a list.
  \begin{enumerate}
  \item Part 1
  \item Part 2 \qedhere
  \end{enumerate}
\end{thm}

Some more text.

\begin{proof}
  Exactly.
\end{proof}

\end{document}

Best Answer

Related Solutions

[Tex/LaTex] amsthm: how to reduce the vertical spacing between theorem and proof

[Tex/LaTex] Indicator at end of theorem

Related Question