\qed for theorems without proofs

Question

It is common to place a \qed-Box at the end of a theorem statement (or lemma, corollary, ...) if we give no proof for that statement.

How can I do this in LaTeX? If I place a qed-box at the end of the statement there is an additional linebreak, which is inacceptable formating.

Answer 1

if you are using amsthm or an ams document class, this problem is addressed by an item in the ams author faq. this in turn links to an example document that covers quite a few of the possible situations in which such a marker could be wanted. the most extreme situations require some manual effort, but i believe that nearly all reasonable possibilities (including the non-proof ending with a display) are covered.

Answer 2

With the theorem packages you would normally use \qed or \qedhere. Without those you use the commands below depending on if you want the filled square or empty:

\documentclass[border=2pt]{standalone}
\usepackage{amssymb}

\newcommand*{\QEDA}{\hfill\ensuremath{\blacksquare}}%
\newcommand*{\QEDB}{\hfill\ensuremath{\square}}%

\begin{document}
Lorem ipsum \QEDA

Lorem ipsum \QEDB

\end{document}

Answer 3

Sometimes it is usefull to create a minimal example:

\documentclass{article}
\usepackage{amsmath,amsthm}
\newtheorem{lem}{Lemma}
\usepackage{lipsum}
\begin{document}
\begin{lem}
Text Text Text \qed
\end{lem}
\end{document}

Answer 4

You could add the \qedsymbol to the end of your theorem automatically. The etoolbox package provides the means to tap into the end of an environment using \AtEndEnvironment{<env>}{<code>}. This adds <code> at \end{<env>}.

\documentclass{article}
\usepackage{amsthm}% http://ctan.org/pkg/amsthm
\usepackage{etoolbox}% http://ctan.org/pkg/etoolbox
\newtheorem{theorem}{Theorem}%
\AtEndEnvironment{theorem}{\null\hfill\qedsymbol}%
\begin{document}
\begin{theorem}
This is an important theorem.
\end{theorem}
\end{document}

However, this is only beneficial if you do not also include a \qedsymbol with your proofs. Moreover, it may cause undesired effects if you end your theorem with an equation. Regardless, you have some options:

• Define a non-proof-theorem environment which adds this automatically; or
• add it manually using some of the other answers provided; or
• provide (say) a starred version of theorem (that is, theorem*) which does the above.

Answer 5

Late to the party, but my answer is as follows:

To insert a QED symbol:

Case 1: Last line of text is to be centre-aligned:

\hfill <last line of code> \hfill $\square$

Case 2: Centre-alignement is not required:

<last line of code> \hfill $\square$

This works inside any environment and even if the last line is an equation, in which case you have to use $\displaystyle <equation>$ instead of \[ \]

Or if you like, use \lozenge instead of $\square$ to have a different QED symbol.

Answer 6

To get the symbol used for typesetting the QED, use \qedsymbol:

\documentclass{minimal}
\usepackage{amsmath,amsthm}
\newtheorem{theorem}{Theorem}
\def\eolqed{\hspace{\stretch1}\ensuremath\qedsymbol}
\begin{document}
\begin{theorem}Foo is a bar.\eolqed
\end{theorem}
\end{document}