I have basically the same question to ask as this MathOverflow question.
I have seen what Tyler says there - I've been playing with it for a few days and unable to work it all out. I thought about registering on MO and just asking on that thread. Unfortunately to leave a comment requires 50 reputation - reputation I can't see myself easily earning just yet.
So is it acceptable to re-ask an MO question here, asking for more details?
Possibly related thread on Math.SE here
Update: The question has been posted: