is mentioned by

Thm* G:(Id), to,from:(|G|(IdLnk List)), e:Edge(G), i:|G|. Thm* bi-graph(G;to;from)  ((inverse(e)  from(i))  destination(e) = i)	[edge-inv-from]
Thm* G:(Id), to,from:(|G|(IdLnk List)), e:Edge(G), i:|G|. Thm* bi-graph(G;to;from)  ((e  from(i))  source(e) = i)	[edge-from]

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