Def Msg(M) == l:IdLnkt:IdM(l,t)

is mentioned by

Def Msg_sub(l; M) == {m:Msg(M)| haslink(l; m) }

[Msg_sub]

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