After discovering <a href="http://docs.mathjax.org/en/latest/tex.html#action">the toggle command</a> available in <a href="http://mathjax.org">MathJax</a>, I immediately went to <a href="http://tex.stackexchange.com/questions/91104/maction-for-pdf-files">asked the capable people</a> of <a href="http://tex.stackexchange.com/">tex.stackexchange</a> whether this could be done inside a PDF file. And indeed: It can be done!
```Latex
\documentclass{article}
\usepackage{animate}
\begin{document}
\begin{animateinline}[step]{1}
\strut$x=1$
\newframe
\strut$x=2$
\newframe
\strut$x=3$
\end{animateinline}
\end{document}
```
Now, what do I want with this package? I want to do <a href="http://en.wikipedia.org/wiki/Abstract_nonsense">abstract nonsense</a>. A diagram-based proof should, in my opinion, be a slideshow. You start with the diagram that is your assumption and by simply interacting with the diagram (clicking it), in each step, a new arrow is constructed from some universal property.
I wanted to write a neat animated PDF with an abstract nonsense proof of the famous <a href="http://en.wikipedia.org/wiki/Snake_lemma">Snake Lemma</a>, and there is a <a href="http://books.google.com/books/about/Handbook_of_Categorical_Algebra_2.html?id=La3gAAAAMAAJ&redir_esc=y">great book by Francis Borceux</a> containing a proof, but <a href="http://math.stackexchange.com/q/314693/11653">unfortunately, I was unable to overcome a difficulty with the proof</a>, so that will have to wait until someone answers my question.