\documentclass[11pt]{article}

\usepackage{amsbsy,amsmath,amsfonts,amsthm}
\usepackage{epsfig}
\usepackage{graphicx} 

\newtheorem{theorem}{Theorem}

\newtheorem{lemma}[theorem]{Lemma}
\newtheorem{proposition}[theorem]{Proposition}
\newtheorem{corollary}[theorem]{Corollary}
\newtheorem{conjecture}[theorem]{Conjecture}
\newtheorem{example}[theorem]{Example}

\theoremstyle{definition}
\newtheorem{definition}[theorem]{Definition}
\newtheorem{remark}{Remark}

\title{}
\author{}
\date{}

\begin{document}
\maketitle



\end{document}