\documentclass{beamer}

\usepackage{beamerthemesplit}
\usetheme{CambridgeUS}

\title{Counting centralizers in nnnnnnnnnnnnnnnnnnnnnnnnnnnnnn}
\author[M.R.R. Mmmmmmmmmmmmmmmm, M. lllllllllllllllllll. S.kkkkkkkkkkkkllllll]
{M.R.R. Mmmmmmmmmmmmmmmm, M. lllllllllllllllllll. S.kkkkkkkkkkkkllllll}
\institute{Speacker}
\date{\today}
\begin{document}

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\frame{\titlepage}
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%\frame{\tableofcontents} %I prefer not to have a table of contents.
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\section{Abstract}
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\section{Introduction}

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\begin{frame}
\frametitle{Lemma}
Similar to group theory 
\begin{lemma}
kkkk
\end{lemma}
\begin{lemma}
llllll
\end{lemma}
\end{frame}
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\begin{frame}
\frametitle{Main Results}
\section{Main Results}

In this
\begin{lemma}

\end{lemma}
\begin{example}

\end{example}
\end{frame}
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\end{document}