Def hd(l) == Case of l; nil  "?" ; h.t  h

is mentioned by

Thm* l:T List, i:||l||, j:i. hd(l_interval(l;j;i)) = l[j]

[hd_l_interval]

In prior sections: mb list 1 list 1

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