Comment 185 for bug 619908

My feeling is that the current behaviour is the not too suprising, but
is perhaps not very "human". Changing it as Abel suggests would, I
think, make the feature more useful without affecting any existing
use-cases.

> Anyway, if we want to keep the current behaviour, we should
> short-cut the long expression to a simple FALSE. (Or is Postgresql
> clever enough to figure this out automatically?)

ISTR that Postgres is clever enough to do this for us, so I kept the
Python implementation as clean and symmetrical as I could.