LaTeX in Ubuntu

Thanks for the replies, everyone. The following is the Preamble of my LaTeX document. Perhaps you could spot an error?

\documentclass[12pt]{amsart}
\newtheorem{definition}{Definition}[section]
\newtheorem{example}[definition]{Example}
\newtheorem{proposition}[definition]{Proposition}
\newtheorem{lemma}[definition]{Lemma}
\newtheorem{remark}[definition]{Remark}
\usepackage{amsmath,mathrsfs}
\usepackage[margin=1in]{geometry}
\newcommand{\Z}{\mathbb{Z}}
\newcommand{\Q}{\mathbb{Q}}
\newcommand{\R}{\mathbb{R}}
\newcommand{\C}{\mathbb{C}}
\newcommand{\N}{\mathbb{N}}
\renewcommand{\baselinestretch}{1.25}