Def e <loc e' == loc(e) = loc(e')  Id & time(e)<time(e')

is mentioned by

Thm* the_w:World, e,e':E. Thm* FairFifo  (e <loc e'  loc(e) = loc(e')  Id & e <c e')	[w-locl-iff]
Def e <c e' == e e,e'. e <loc e'  isrcv(kind(e')) & e = sender(e')  E^+ e'	[w-causl]

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