[leafnode-list] filtering crossposts

[Amedee Van Gasse]

Hello,

I would like to filter messages that are crossposted between certain
groups, but not the groups themselves.
With an example: I want to see posts that go to be.comp.os.linux OR to
be.comp.os.windows, but I don't want to see posts that are crossposted
between them (because these are almost always inflamatory...)

I suppose I need to cast some arcane regex-runes to accomplish this, but
my regex-fu is rather weak. Could someone please help? I only need a
good example to get started.

Anyway, thanks for your attention.

-- 
Amedee Van Gasse
amedee at amedee.be