Some definitions of interest.
inv_funs_2	Def  InvFuns(A;B;f;g) == (x:A. g(f(x)) = x) & (y:B. f(g(y)) = y)
	Thm*  f:(AB), g:(BA). InvFuns(A;B;f;g)  Prop
sq_stable	Def  SqStable(P) == P  P
	Thm*  A:Prop. SqStable(A)  Prop

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