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A "Proof of" environment

When I have a long proof in a paper that I want to push to another section, I want a theorem-style environment that produces "Proof of ..." and drops a QED symbol at the end. One way to do this is to use amsthm to declare proof environments. Write

\theoremstyle{plain}
\newtheorem{thm}{Theorem}
\theoremstyle{definition}
\newtheorem*{proof1}{Proof of Theorem \ref{Fermat}}

in the preamble, and use the thm environment for the theorem, and then proof1 for the proof, and be sure to put \qed at the end of the proof.

If you have a lot of proofs, this is tedious, and the QED symbol at the end is not perfect, particularly when you are ending the proof with a displayed equation and want to use \qedhere. Here is a bit of a hack which does everything we need. The entire example:

\documentclass[a4paper]{article}

\usepackage{amsthm}

\theoremstyle{plain}
\newtheorem{thm}{Theorem}

% for use with amsthm
% same as proof environment, but with definition-style proof head
% and named theorem.
\makeatletter
\newenvironment{proofof}[1]{\par
\pushQED{\qed}%
\normalfont \topsep6\p@\@plus6\p@\relax
\trivlist
\item[\hskip\labelsep
\bfseries
}{%
\popQED\endtrivlist\@endpefalse
}
\makeatother

\begin{document}

\begin{thm}\label{Fermat}
No natural numbers $a,\,b,\,c$ can satisfy the equation $a^n+b^n=c^n$
for integer $n > 2$.
\end{thm}

We postpone the proof until later.

% Time passes...

\begin{proofof}{Theorem \ref{Fermat}}
(Insert 100 pages of complicated mathematics here.)
\end{proofof}

\end{document}

As usual, this is too complex for the wiki to parse, but it produces Fermat's last theorem, followed by a definition-style "Proof of Theorem 1", the proof, and then a QED symbol. And you can use \qedhere just as you would in the amsthm proof environment.

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