# qed symbol error

I may have misunderstood the documentation, but I believe that if I use the amsmath package in the declaration, then typing \qed should give me a Q.E.D. symbol. When I do this, it crashes with undefined control sequence.

The snippet:

\documentclass[11 pt]{article}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{graphicx}
\graphicspath{{/texfiles/}}
\begin{document}
...
Since we proved that any function with the property ($\pi$) is an increasing involution, we have thus proved that $f(x) = x$ is the only function which satisfies ($\pi$).
\qed


What is going wrong here?

-

You need the amsthm package for that:

\documentclass[11 pt]{article}
\usepackage{amsmath,amsthm}
\usepackage{amsfonts}
\usepackage{graphicx}
\graphicspath{{/texfiles/}}
\begin{document}
...
Since we proved that any function with the property ($\pi$) is an increasing involution,
we have thus proved that $f(x) = x$ is the only function which satisfies ($\pi$).
\qed
\end{document}

-
Thank you! Can I adjust the symbol's placement? (Edit: never mind, I found that out. Thank you!) – user1296727 Jul 30 '12 at 5:35
You may add that the QED symbol is added automatically in the proof environment and that there's \qedhere for particular cases, when the proof ends with an alignment environment or a list. – egreg Jul 30 '12 at 9:41