indentationtheorems
I'm using amsbook document class and amsthm package. I want the proofs to stand out from the rest of the text by slightly indenting them, i.e. leaving some margins from left and right. How do I do that?
It seems that Margins for proof environment is the same question. But the code doesn't work for me, probably because I'm using amsthm package already.
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}
Here's one approach, that uses etoolbox to tweak the definition of \FrameCommand from within the outermost theorem. A complete MWE follows:
\documentclass{article}
\usepackage[framed]{ntheorem}
\usepackage{framed} % To define \FrameCommand
\usepackage{color} % To define \definecolor
\usepackage{lipsum} % For the dummy text
\definecolor{gray}{rgb}{0.6,0.6,0.6}
\usepackage{etoolbox} % For \appto
\theoremstyle{plain}
\newframedtheorem{thm}{Theorem}[page]
\renewcommand*\FrameCommand{\relax} % By default, no framing occurs
\appto\thm{% ... but within the thm environment, FrameCommand is different
\renewcommand*\FrameCommand{{\color{gray}\vrule width 5pt \hspace{10pt}}}
}
\begin{document}
\noindent \lipsum[1]
\begin{thm}
Outer theorem
\begin{thm}
Theorem nested once
\begin{thm}
Theorem nested twice
\end{thm}
\end{thm}
\end{thm}
\end{document}
This results in the following appearance:
You'd need to add a similar call to \appto for each additional environment for which you wanted such nesting behavior. (Unfortunately, the original solution I proposed, using AtBeginEnvironment adds the hook too early in the environment definition, so the FrameCommand gets redefined before it's used in the outermost environment too. This version, using \appto\thm, is slightly less polite in that it hacks the opening of the environment by modifying the \thm command directly, but it adds the hook at the right moment.)
Best Answer
You can experiment with this modification of the
proofenvironment:However it doesn't seem a good idea to me: if the proof is short it's easily recognizable anyway; if it's long, the narrow margin will spoil the page balance.