Def deq-member(eq;x;L) == reduce(a,b. eqof(eq)(a,x)  b;false;L)

is mentioned by

Def x  dom(f) == deq-member(eq;x;1of(f))

[fpf-dom]

In prior sections: mb event system 2

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