Def Unit == 0  

is mentioned by

Thm* SQType(Unit)	[sfa_doc_sqtype_unit]
Def A^n == if n=0 Unit ; n=1 A else A(A^(n-1)) fi  (recursive)	[sfa_doc_ntuple]

In prior sections: core bool 1

IF YOU CAN SEE THIS go to /sfa/Nuprl/Shared/Xindentation_hack_doc.html