14  Overlays

Probably the most interesting effect achieved by Beamer is overlays, which gives the appearance of incremental exposure of a given slide.

Achieving the overlay effect in Beamer is quite simple—just insert a \pause command anywhere you want to pause the display.

For instance, to expose an itemized list one-item-at-a-time, do:

\documentclass{beamer} 
\usetheme{default} 
\begin{document} 
 
\begin{frame}{Outline of the talk} 
 
\begin{itemize} 
  \item Introduction 
  \pause 
  \item Statement of the main theorem 
  \pause 
  \item Technical lemmata 
  \pause 
  \item Proof of the main theorem 
  \pause 
  \item Conclusions 
\end{itemize} 
 
\end{frame} 
 
\end{document} 

When this file is compiled into the pdf format and displayed with a pdf viewer, such as the Acrobat Reader, the items are exposed one-at-a-time as you page forward through the document in the usual way.

The use of the \pause command is not restricted to itemized lists; you may use it anywhere in a slide. For example:

\documentclass{beamer} 
\usetheme{Malmoe} 
\begin{document} 
 
\begin{frame}{Fermat's Last Theorem} 
 
In this talk I will give a very elementary proof of the 
theorem.  I am surprised that no one else has thought of 
this before. 
\medskip 
 
\pause 
 
Fermat's Last Theorem says that the equation 
\[ 
  x^2 + y^2 = z^2 
\] 
has no solution in the set of natural numbers. 
\medskip 
 
\pause 
 
This is not true.  After a lengthy calculation on the 
department's Linux machines, I have verified that within 
the numerical accuracy of the Pentium-4 processor, we have: 
\[ 
  5000^2 + 12000^2 = 13000^2 
\] 
 
\end{frame} 
 
\end{document} 

A pdf viewer will expose the resulting file one paragraph at a time. The fully exposed slide looks like this: