Denoting the end of example/remark

Question

What is the etiquette to denote the end of an example or remark? For proofs, it's the QED symbol (white box). I know it's not necessary for everyone, but I would like to use it to break up the text a little. What should I use? A circle or filled box or what?

Answer 1

I think this is totally a matter of personal style. If you are using \qed already you could use a similar symbol like \triangle.

Whatever you do, don't just use \hfil$\triangle$ because this does not work when your example fills the last line completely. Here is a definition of \demo that uses the flexible \xqed:

\documentclass{minimal}
\usepackage[utf8]{inputenc}

\newcommand\xqed[1]{%
  \leavevmode\unskip\penalty9999 \hbox{}\nobreak\hfill
  \quad\hbox{#1}}
\newcommand\demo{\xqed{$\triangle$}}

\begin{document}
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam.
\demo    
\end{document}

The manfnt font also provides also a filled triangle pointing to the right. After declaring \font\manual=manfnt you can use \manual\char'170.

Answer 2

Try the following indirect method (requires amsthm):

\newtheorem{examplex}{Example}
\newenvironment{example}
  {\pushQED{\qed}\renewcommand{\qedsymbol}{$\triangle$}\examplex}
  {\popQED\endexamplex}

In this way also \qedhere works exactly like in proof.

Answer 3

Maybe you’ll like to use the {leftbar}-environment?

\documentclass{minimal}
\usepackage{framed}
\begin{document}
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam.
\begin{leftbar}
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam.
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam.
\end{leftbar}
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam.
\end{document}

If you like it I can show an extended example with a colored bar, no indention of first line an support for floating objects in the environment.

Answer 4

The very useful thmtools package has a key for defining the qed-symbol. For example, I use the following in my documents:

\usepackage{amsthm,thmtools}
\theoremstyle{remark}
\declaretheorem[name=Example,qed={\lower-0.3ex\hbox{$◃$}}]{Ex}

...

\begin{Ex}
  The numbers 2, 3 and 5 are all prime.
\end{Ex}

(I use unicode-math to be able to use the ◃ symbol directly. Just replace it by whatever symbol you like, e.g. \triangleleft.)

Everything is set up correctly so that you can use \qedhere like in a standard amsthm proof environment.