Thanks to an answer to my question asked here, I used the following codes to generate for each theorem-alike environment exactly one square symbol as the ending sign:
\documentclass[12pt]{amsart}
\usepackage{manfnt}
\makeatletter
\renewcommand\@endtheorem{\vvv@endmarker\endtrivlist\@endpefalse}
\newcommand\vvv@endmarker{%
{\unskip\nobreak\hfil\penalty50
\hskip2em\vadjust{}\nobreak\hfil\openbox
\parfillskip=0pt \finalhyphendemerits=0 \par
\penalty 10000 \parskip=0pt\noindent}\ignorespaces}
\makeatother
\newtheorem{thm}{Theorem}
\begin{document}
\title[]{Title}
\author[]{Author}
\maketitle
\section{Proofs}
... The above argument proves the following theorem:
\begin{thm}
There are infinitely many integers $x, y, z > 0$ such that
\[ x^{2} + y^{2} = z^{2}.\]
\end{thm}
\end{document}
However, how do I make the square symbol, the ending sign, lie within the displayed equation? I tried \qedhere but nothing happened.
\newmarkedtheoremmethod that's not working for you? – Mico May 29 '15 at 06:26