# beamer — making visible a part of an invisible block (theorem)

I have the following problem:

I have a theorem and want to show only one part of it first, without showing the head of the theorem. I tried:

\documentclass[11pt]{beamer}
\usetheme{Malmoe}
\usepackage[utf8]{inputenc}
\usepackage[german]{babel}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{graphicx}

\begin{document}

\begin{frame}{A title}
\onslide<1->{Motivational text.}
\visible<3->{
\begin{theorem}
We have that
\begin{align*}
\visible<2->{\sqrt{\pi}} = \int_{-\infty}^\infty e^{-x^2} \text{d} x
\end{align*}
\end{theorem}}
\end{frame}

\end{document}


what I get:

what I want:

EDIT:

the improved code

\documentclass[11pt]{beamer}
\usetheme{Malmoe}
\usecolortheme{seagull}
\usepackage[utf8]{inputenc}
\usepackage[german]{babel}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{xcolor}

\begin{document}

\definecolor{seagullgray}{HTML}{CCCCCC}

\begin{frame}{A title}
\onslide<1->{Motivational text.}
\only<1-2>{\setbeamercolor{block title}{fg=seagullgray}}
\begin{theorem}
\visible<3->{We have that}
\begin{align*}
\visible<2->{\sqrt{\pi}} \visible<3->{= \int_{-\infty}^\infty e^{-x^2}\text{d} x}
\end{align*}
\end{theorem}
\end{frame}

\end{document}


yields

In this compiler the color #CCCCCC doesnt even seem to fit.

Maybe a bit hacky but one could simply change the colour of the title to hide it:

\documentclass[11pt]{beamer}
\usetheme{Malmoe}
\usepackage[utf8]{inputenc}
\usepackage[german]{babel}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
%\usepackage{graphicx}

\begin{document}

\begin{frame}{A title}
\onslide<1->{Motivational text.}
\only<1-2>{\setbeamercolor{block title}{fg=bg}}
\begin{theorem}
\visible<3->{We have that}
\begin{align*}
\visible<2->{\sqrt{\pi}} \visible<3->{= \int_{-\infty}^\infty e^{-x^2} \text{d} x}
\end{align*}
\end{theorem}
\end{frame}

\end{document}


With another colour theme:

\documentclass[11pt]{beamer}
\usetheme{Malmoe}
\usecolortheme{seagull}
\usepackage[utf8]{inputenc}
\usepackage[german]{babel}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
%\usepackage{graphicx}
%\usepackage{xcolor}

\begin{document}

\begin{frame}{A title}
\onslide<1->{Motivational text.}
\only<1-2>{%
\setbeamercolor{block title}{fg=bg,bg=bg}
\setbeamercolor{block body}{bg=bg}
}
\begin{theorem}
\visible<3->{We have that}
\begin{align*}
\visible<2->{\sqrt{\pi}} \visible<3->{= \int_{-\infty}^\infty e^{-x^2}\text{d} x}
\end{align*}
\end{theorem}
\end{frame}

\end{document}


Off-topic: You don't need \usepackage{graphicx} nor \usepackage{xcolor} with beamer

• Wow! I have not such good imagination and was developing a tikz overlay solution. (+1) – koleygr Sep 8 '18 at 14:33
• This is a good idea. But unfortunately I use the colortheme seagull. There the Theorem environment has a gray background. I adapted your answer to this insofar that I set the block title color to #CCCCCC. (+1). But the background stays gray of course. – Falrach Sep 8 '18 at 14:36
• @Falrach If you could make a MWE that demonstrated the problem, I'm sure it can be fixed. – samcarter_is_at_topanswers.xyz Sep 8 '18 at 14:58
• @koleygr Thanks for the vote. Using tikz overlay is actually also a very good idea. If you already have something it might be interesting to post it as an answer - I would surely upvote it! – samcarter_is_at_topanswers.xyz Sep 8 '18 at 15:04
• @samcarter I have edited my answer and added the adapted code. – Falrach Sep 8 '18 at 15:13