LaTeX proof environment

Everyone seems to have their own way of making a proof environment in LaTeX, so here is mine!

Something of a novelty is the automatic positioning of the end-of-proof symbol on the last line of the proof, even if the last line is inside a dsiplayed equation or a list.

All the magic is in the ntheorem package, it just doesn't seem to be very well known.

\usepackage[amsmath,thmmarks]{ntheorem}
% option amsmath is not necessary if you are not using amsmath.
% If you are using amsmath, then include it before ntheorem.

\theoremstyle{nonumberplain}
\theoremheaderfont{\bfseries}
\theorembodyfont{\normalfont}
\theoremseparator{.}
\theoremsymbol{\ensuremath{\square}}
\newtheorem{proof}{Proof}

% On an unrelated note, I INSIST THAT YOU
\renewcommand{\leq}{\leqslant}
\renewcommand{\le}{\leqslant}
\renewcommand{\geq}{\geqslant}
\renewcommand{\ge}{\geqslant}
% (which needs amssymb)