\documentclass[12pt,letterpaper]{article}
\usepackage[latin1]{inputenc}
\usepackage[letterpaper,twosideshift=.2in,dvips, includemp=false,tmargin=1in,bmargin=1in, width=3in]{geometry}
\usepackage[dvips]{graphicx}
\newcommand{\betweenLilyPondSystem}[1]{\linebreak}
\begin{document}
\newcommand{\composer}[1]{\begin{flushright}{\textsl{#1}}\end{flushright}}
\newcommand{\lilytitle}[2]{\begin{center}{\LARGE{\textbf{#1}}\\\Large{#2}}\end{center}}
\newcommand{\lilycontentsline}[1]{\addcontentsline{toc}{section}{#1}}
\lilycontentsline{}

\lilypondfile[staffsize=20]{cantus.ly}

\end{document}