# Creating a hidden (unlisted) section and not breaking the current subsection

## The Problem

In my presentation, I want to incorporate a small crash-course inside a specific subsection. This crash-course should have no own section, but should be outside the current section and subsection. Kind of like the appendix, but the TOC should still be visible, just completely greyed out.

After slide 1 of the subsection I want to have one or two slides hidden from all content listings (maybe excluding overall page numbering) and after that, I will continue with slide 2 from the subsection I left. This isn't conditional, so a button to a slide in the appendix won't help me and I don't want to have to click on the slide during the talk.

## Ideas

I tried to hide the slides in an unlisted section, but this breaks the counter of the frames inside the subsection - obviously, since I ended the subsection with a new section. There should be a counter I can set, but I don't know which one.

Additionally, it would be cool if the hidden section, while showing the overall TOC, could have a subsection title in the corresponding line - but this isn't crucial.

## MWE

\documentclass[a4paper]{beamer}

\usetheme{Dresden}
\usecolortheme{albatross}

\begin{document}
\section{Main section}
\subsection{First subsection}
\begin{frame}{First frame of first subsection}
People understand all this stuff.
\end{frame}
\section[]{Hidden crash-course}
% IT WOULD BE NICE TO HAVE AN SUBSECTION TITLE HERE
\begin{frame}{Explain stuff to me}
You will need this and that for the next slide
\end{frame}
% \section{Main section} SHOULD BE CONTINUED HERE
\subsection{First subsection (don't break me)}
\begin{frame}{Second frame of first subsection}
Luckily you paid attention to the crash-course, so now you understand this...
\end{frame}
\begin{frame}{Third frame of first subsection}
... and that.
\end{frame}
\subsection{Second subsection}
\begin{frame}{Some different stuff}
Content
\end{frame}
\end{document}

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