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)