# \newtheorem with qed-symbol

Is there a pre-defined theorem-environment for a theorem having the qed-symbol at its end?

Something like the proof-environment but with the \theoremstyle{plain}?

\documentclass{scrartcl}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage{amssymb,amsmath}
\usepackage{amsthm}
\usepackage{dsfont}
\usepackage{empheq}
\theoremstyle{plain}
\newtheorem{theo}{theorem}

\begin{document}
\begin{theo}
One theorem.
\end{theo}
Some text.
\begin{proof}
One proof.
\end{proof}
\end{document}


In my code: I am looking for the theo-layout but with a sqare at its end.

I suggest to have a theo environment and a theo* environment for theorems which don't need a proof. Using the tombstone for all theorem statements doesn't seem a good idea, because theorem statements, contrary to proofs, are well delimited.

\documentclass{scrartcl}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage{amssymb,amsmath}
\usepackage{amsthm}
\usepackage{dsfont}
\usepackage{empheq}
\theoremstyle{plain}

\newtheorem{theo}{Satz}
\newenvironment{theo*}
{\pushQED{\qed}\theo}
{\popQED\endtheo}

\begin{document}
\begin{theo*}
This requires no proof.
\end{theo*}

\begin{theo}
One theorem.
\end{theo}
Some text.
\begin{proof}
One proof.
\end{proof}
\end{document}


The tac.cls document style at http://www.tac.mta.ca/tac/style/tac.cls includes a proof environment with a Halmos QED. The amsthm package has a proof environment with a hollow QED symbol. Not quite what you want, but maybe it will help.

BTW, the acronym QED stands for quod erat demonstrandum, and as such is only appropriate after a proof.