Graphics, Figures & Tables ⇒ Add a Frame to a Proof

[TesTT]

Hey,

In university I learned to write theorems and proofs as shown in the attached picture. Now I started typing my own lecture notes and was wondering how one could accomplish such a "frame" around the edges of the proof.

Thanks for your help.

[cgnieder]

I'd do this kind of things with mdframed. when used with framemethod=tikz the corners of the environment can be accessed with TikZ. Details on the package can be read in the documentation (mdframed).

Code: Select all

\documentclass{article}

\usepackage{amsmath,amsthm}
% upright instead of italic text in the theorem:
% \theoremstyle{definition}
% new theorem:
\newtheorem{thm}{Theorem}

% closed box instead of open box for the qed symbol:
\newcommand*\closedbox{%
  \leavevmode\hbox to.77778em{\hfil\rule{.675em}{.675em}\hfil}}
\let\qedsymbol\closedbox


\usepackage[framemethod=tikz]{mdframed}
% new mdframed style that places the edges at the corners:
\mdfdefinestyle{proof}{
  skipabove         = .5\baselineskip ,
  skipbelow         = .5\baselineskip ,
  leftmargin        = 0pt ,
  rightmargin       = 0pt ,
  innermargin       = 0pt ,
  innertopmargin    = .5em ,
  innerleftmargin   = .5em ,
  innerrightmargin  = 0pt ,
  innerbottommargin = 0pt ,
  hidealllines      = true ,
  singleextra       = {
    \draw (O) -- ++(0,.675em) (O) -- ++(.675em,0) ;
    \draw (P-|O) -- ++(0,-.675em) (P-|O) -- ++(.675em,0) ;
  },
  firstextra        = {
    \draw (P-|O) -- ++(0,-.675em) (P-|O) -- ++(.675em,0) ;
  },
  secondextra       = {
    \draw (O) -- ++(0,.675em) (O) -- ++(.675em,0) ;
  },
}
% put the new mdframed style around the proof environment:
\surroundwithmdframed[style=proof]{proof}

\usepackage{lipsum}% dummy text

\begin{document}    

\begin{thm}
 \lipsum[2]
\end{thm}

\begin{proof}
 \lipsum[2]
\end{proof}

\end{document}

proof.png (46.46 KiB) Viewed 10095 times

Regards

[TesTT]

Thanks a lot for your reply. But is there an equivalent for Miktex?

[cgnieder]

But is there an equivalent for Miktex?

I don't understand... why would it be any different with MiKTeX than any other TeX distribution? This code is independent of the TeX distribution as long it is up to date (and possibly complete).

Regards

[TesTT]

Well, I received the following error messages when I tried your code. Hence I assumed it could only be used with certain latex libraries (since you mentioned TikZ). :/

[cgnieder]

I guess you need to update your distribution. The current version of mdframed is 1.6d. Yours seems to be too old (can't say definitely -- you should be able to find the information in the log file, though).

Regards

[TesTT]

Thanks for the tip. It works perfectly now.

[TesTT]

Just one little additional question: how can i indent the text after the first line (as shown in the screenshot), i.e. keep the red-shaded areas clear of any text?