Some definitions of interest.
sfa_doc_factorial	Def x! == if x=0 1 else x(x-1)! fi  (recursive)
	Thm* x:. x!
eq_int	Def i=j == if i=j true ; false fi
	Thm* i,j:. (i=j)
nat	Def  == {i:| 0i }
	Thm*   Type
nequal	Def a  b  T == a = b  T
	Thm* A:Type, x,y:A. (x  y)  Prop

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