The beamer class Manual for version 3.06. \begin{frame} \frametitle{There Is No Largest Prime Number} \framesubtitle{The proof uses \textit{reductio ad absurdum}.} \begin{theorem} There is no largest prime number. \end{theorem} \begin{proof} \begin{enumerate} \item<1-| alert@1> Suppose $p$ were the largest prime number. \item<2-> Let $q$ be the product of the first $p$ numbers. \item<3-> Then $q+1$ is not divisible by any of them. \item<1-> Thus $q+1$ is also prime and greater than $p$.\qedhere