[Tex/LaTex] placement of QED symbol on numbered equation line

equationstheorems

This question is both on LaTeX and on mathematics writing style; I hope that's still apropriate here.

I have a proof that ends with a (right) numbered equation, and I'm pondering about where to put the QED symbol. The standard right margin position conflicts with the equation number, so what would be considered best style for the QED placement?

Secondly, I use the ntheorem package, but cannot place the QED symbol using \qedhere on this equation line. Is there a (simple) way to solve this?

Best Answer

I have the following two suggestions:

  1. Reword your proof. Even if you merely state the obvious:

    ...
        x^n + y^n = z^n
which completes the proof.

    or

    Proof. It follows trivially that for
        x^n + y^n = z^n
there exist no solutions.

  2. Place the QED symbol manually next to the equation and correct for horizontal alignment with \phantom or use \rlap. Hopefully this is not something that has to be done frequently.

    enter image description here

    \documentclass[a4paper,11pt]{article}

\usepackage{amsmath,amssymb}
\usepackage[thmmarks,amsmath,amsthm,hyperref]{ntheorem}

\newtheorem{theorem}{Theorem}[section]
\begin{document}

\begin{proof}
  foo.
\end{proof}

\begin{proof}
  It follows trivially that no solutions exist for
  \begin{equation*}\label{eq:fermat1}
    x^n + y^n = z^n.
    \refstepcounter{equation}
    \tag*{(\theequation)}
  \end{equation*}
\end{proof}

\begin{proof}
  It follows trivially that no solutions exist for
  \begin{equation}\label{eq:fermat2}
    x^n + y^n = z^n. \rlap{$\qquad \Box$}
  \end{equation}
\end{proof}

\end{document}
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