is mentioned by

Thm* es:ES, i:Id, P:({e:E| loc(e) = i  Id }Prop). Thm* e@i.P(e)  e@i.first(e)  P(e) & e@i.first(e)  P(pred(e))  P(e)	[alle-at-iff]
Thm* es:ES, x:Id, e:E. Thm* first(e)  (x after pred(e)) = (x when e)  vartype(loc(e);x)	[es-after-pred]
Def before(e) == if first(e) nil else before(pred(e)) @ [pred(e)] fi Def (recursive)	[es-before]

In prior sections: mb event system 2

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