[Pan-users] Rule to block crossposts

[Daniel Mahoney]

I've been running Pan as my newsreader for a couple years and I've been 
using the "Filters" tool to plonk spammers, etc. Now I'd like to figure 
out how to block crossposted messages.

My googling suggests that I need to write a rule to describe crossposts. 
I've looked at several pages describing how to write slrn rule files, 
but I've also read that slrn regexs and pan regexs differ somewhat. And 
I haven't seen anything that shows clearly how to detect crossposts.

I have seen a specific example that shows how to detect messages 
crossposted to a specific group, but I want to ignore any message posted 
to more than one group (I know, that's a perfectly valid and often tool, 
but the groups I hang out in don't lend themselves to use of crossposting).

If worse comes to worst I'll start looking at the source code and create 
myself a tool to do what I want, but I'm sure that someone out there has 
done this before. Could anyone point me to pages where I might learn 
morea bout writing Pan rules, or perhaps even explicitly to a page that 
shows me how to do what I'm trying to accomplish?