\documentclass[leqno]{article}

\usepackage[paperwidth=500cm,textwidth=495cm]{geometry}
\usepackage[utf8]{inputenc}
\usepackage{amssymb}
\usepackage{latexsym}
\usepackage{amsmath}
\usepackage{proof}
\usepackage{color}
\usepackage{moreverb}
\usepackage{array}
\usepackage{bm}
\newcommand{\Boxd}{\Box^{\downarrow}}
\newcommand{\bs}{\backslash}
\newcommand{\bo}{[}
\newcommand{\bc}{]}

\definecolor{gray80}{gray}{0.80}

\begin{document}

\input{proof}

\end{document}