Def isl(x) == InjCase(x; y. true; z. false)

is mentioned by

Def isnull(a) == isl(a)

[w-isnull]

In prior sections: union mb event system 1

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