R help - Oct 2005 - using markstat

Dear all,
I am using the spatstat package, and in particular the algorithm 

markstat(X,fun,N,R,.)

I need that output to detect which is the nearest neighbour of each point in
that point pattern.

Therefore, I would use
 X=my ppp object already defined,
 N=2
But what function should I use? It should be something like "none"..?!

Hope you can help me on this.

Regards,
Sara Mouro

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