I'm reading through a book, and it walks through a problem. We need to compute $p(a | e, f)$. It says that by applying the chain rule we can see:
$p(a|e,f) = \frac{p(e,a|f)}{p(e|f)}$
Looking at the chain rule, I do not understand how that was arrived at.
I imagine there is a simple explanation (since no further working was shown in the book), is anyone able to provide one?