Long equation does not page break

Question

I have a series of equations steps, about 20 lines or so. I would like to have it automatically decide page break when necessary, but it resists and always tries to stay in a whole page, rendering the previous page a lot of while space.

I tried \allowdisplaybreaks and \displaybreak, but doesn't seem to work.

{\allowdisplaybreaks\begin{equation}\allowdisplaybreaks[4]
\begin{split}\allowdisplaybreaks
\alpha\beta\gamma&=abc\\
=def\\
=ghi\\
\end{split}
\end{equation}}

Answer 1

From page 6 of the amsmath manual:

Certain equation environments wrap their contents in an unbreakable box, with the consequence that neither \displaybreak nor \allowdisplaybreaks will have any effect on them. These include split, aligned, gathered, and alignedat.

Put differently, use an align environment -- along with something like \allowdisplaybreaks.

Personally I always try to break up long sequences of equations with a few words or sentences.