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

Try the following indirect method (requires amsthm):

\newtheorem{example}{Example}
\AtBeginEnvironment{example}{%
  \pushQED{\qed}\renewcommand{\qedsymbol}{$\triangle$}%
}
\AtEndEnvironment{example}{\popQED\endexample}

Full example

\documentclass{article}
\usepackage{amsmath,amsthm}
% some setup
%
% maybe change here the default symbol
% \renewcommand{\qedsymbol}{...}
%
\NewCommandCopy{\proofqedsymbol}{\qedsymbol}% save the default
\newcommand{\exampleqedsymbol}{$\triangle$}% for end of examples
% ensure that proof has the standard symbol
\AtBeginEnvironment{proof}{\renewcommand{\qedsymbol}{\proofqedsymbol}}
% define an environment for examples
\theoremstyle{definition}
\newtheorem{example}{Example}
\AtBeginEnvironment{example}{%
  \pushQED{\qed}\renewcommand{\qedsymbol}{$\triangle$}%
}
\AtEndEnvironment{example}{\popQED\endexample}
\begin{document}
\begin{example}
This has only text.
\end{example}
\begin{example}
This has text but also a proof inside it.
\begin{proof}
This is the proof of the above claim.
\end{proof}
And now the example is over.
\end{example}
\begin{example}
This has also a display at the end:
\begin{align}
f(x) &= \bigl( g(x) \bigr) \
h(x) &= \bigl( r(x) \bigr).\qedhere
\end{align}
\end{example}
\end{document}

LaTeX has now incorporated \AtBeginEnvironment and \AtEndEnvironment that used to be only available with etoolbox.

Original answer

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.

Full example.

\documentclass{article}
\usepackage{amsmath,amsthm}
\theoremstyle{definition}
\newtheorem{examplex}{Example}
\newenvironment{example}
  {\pushQED{\qed}\renewcommand{\qedsymbol}{$\triangle$}\examplex}
  {\popQED\endexamplex}
\begin{document}
\begin{example}
This has only text.
\end{example}
\begin{example}
This has also a display at the end:
\begin{align}
f(x) &= \bigl( g(x) \bigr) \
h(x) &= \bigl( r(x) \bigr).\qedhere
\end{align}
\end{example}
\end{document}

Answer 2

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

Answer 3

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.

Answer 4

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 5

Use \qed right before \end{example} :

\newtheorem{example}[definition]{Example}
.
.
.
\begin{example}
5+6=11
\qed
\end{example}