\newtheorem{theorem}{Theorem}[section]
\newtheorem{lemma}[theorem]{Lemma}
\newtheorem{corollary}{Corollary}[theorem]

\begin{document}
\maketitle
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\section{} %Problem 1
\subsection{Prompt}
\kant%


\noindent\rule{2in}{0.4pt}
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\end{document}