is mentioned by

Thm* a,b:Id. a = b  a = b	[assert-eq-id]
Thm* a:Id. a = a ~ true	[eq_id_self]
Def has-src(i;k) == isrcv(k)source(lnk(k)) = i	[has-src]

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