Some definitions of interest.
nat	Def  == {i:| 0i }
	Thm*   Type
sfa_doc_factorial	Def x! == if x=0 1 else x(x-1)! fi  (recursive)
	Thm* x:. x!

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