is mentioned by

Thm* L:T List, x:T. null(L)  last([x / L]) = last(L)	[last_cons]
Thm* T:Type, L:T List. null(L)  last(L)  T	[last_wf]

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