# [FOM] P-point/notation

T.Forster@dpmms.cam.ac.uk T.Forster at dpmms.cam.ac.uk
Thu May 21 15:39:51 EDT 2009

I hope you will get a reply from someone better informed than i...

My understanding is that the terminology comes from banach spaces: a
p-point is a point such that a countable intersection of neighborhoods of
it is also open. P-point ultrafilters have this property in the usual
(stone) topology on ultrafilters.

But, as i say, i hope you will get a fuller story from an expert.

On May 21 2009, pax0 at seznam.cz wrote:

> Hi, can someone please tell me, why certain ultrafilters on \omega are
> called "P-points" : what "P" means here? And the associated property of
> forcing notions, the "PP property": what "PP" stands for here? I would
> just like to know what are these named after, not any definitions. Thank
> you, Jan Pax _______________________________________________ FOM mailing
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