# Parallel overlays in Beamer

I have 2 columns of blocks side by side in 1 slide:

\begin{columns}
\begin{column}{0.48\textwidth}
\begin{block}{left block 1}
left block 1
\end{block}
\begin{block}{left block 2}
left block 2
\end{block}
\end{column}
\begin{column}{0.48\textwidth}
\begin{block}{right block 1}
right block 1
\end{block}
\begin{block}{right block 2}
right block 2
\end{block}
\end{column}
\end{columns}


What I would like to realize is: left block 1 and right block 1 are shown initially, when I left-click the mouse, left block 2 and right block 2 are shown at the same time under them.

I don't know if it is possible to do it by onslide or pause... Could anyone help?

-

Just add overlay specifications to the lower blocks, as in:

\documentclass{beamer}
\begin{document}
\begin{frame}
\begin{columns}
\begin{column}{0.48\textwidth}
\begin{block}{left block 1}
left block 1
\end{block}
\begin{block}<2>{left block 2}
left block 2
\end{block}
\end{column}
\begin{column}{0.48\textwidth}
\begin{block}{right block 1}
right block 1
\end{block}
\begin{block}<2>{right block 2}
right block 2
\end{block}
\end{column}
\end{columns}
\end{frame}
\end{document}

-
Thank you... What if the "lower blocks" are not "block"? I mean, sometimes I just want to show two sentences left sentence 2 and right sentence 2, it seems that <2>left sentence 2 or <2>right sentence 2 does not work... –  SoftTimur Aug 15 '12 at 14:57
The command \only is overlay-specification aware, for example, \only<2>{left sentence 2} etc. Note that if you want different portions of text to appear on different slides, you need to modify the overlay specifications accordingly. E.g. you might use <2-> to mean the overlay should start on slide 2 and remain, or <3> to mean shown only on slide 3. –  cyberSingularity Aug 15 '12 at 15:00