Some definitions of interest.
assert	Def b == if b True else False fi
	Thm* b:. b  Prop
iff	Def P  Q == (P  Q) & (P  Q)
	Thm* A,B:Prop. (A  B)  Prop
rev_implies	Def P  Q == Q  P
	Thm* A,B:Prop. (A  B)  Prop

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