Def upto(n) == if n=0 nil else upto(n-1) @ [(n-1)] fi  (recursive)

is mentioned by

Def rcvs(l;t) == filter(a.isrcv(l;a);map(t1.a(destination(l);t1);upto(t)))	[w-rcvs]
Def snds(l;t) == concat(map(t1.m(l;t1);upto(t)))	[w-snds]

In prior sections: mb event system 1

Try larger context: EventSystems IF YOU CAN SEE THIS go to /sfa/Nuprl/Shared/Xindentation_hack_doc.html