Searching for paper about pg's optimizer cost model - Mailing list pgsql-general

Hello,

does anybody know a paper (or any document but the code itself) containing a
description of the current cost model used by the query optimizer/planner.
I'm about to write a master thesis in this area that aims for more exact
estimates. Best would be some mathematical formulas with a rationale, but
anything else would help, too.

Regards,
Daniel Bausch
TU-Darmstadt (Germany)