Some definitions of interest.
absval	Def |i| == if 0i i else -i fi
	Thm* x:. |x|
divides	Def b | a == c:. a = bc
	Thm* a,b:. (a | b)  Prop
iff	Def P  Q == (P  Q) & (P  Q)
	Thm* A,B:Prop. (A  B)  Prop
nat	Def  == {i:| 0i }
	Thm*   Type

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