Some definitions of interest.
bijection_type	Def  A bij B == {f:(AB)| Bij(A; B; f) }
	Thm*  A,B:Type. A bij B  Type
int_seg	Def  {i..j} == {k:| i  k < j }
	Thm*  m,n:. {m..n}  Type
inv_pair	Def  AB == {fg:((AB)(BA))| fg/f,g. InvFuns(A;B;f;g) }
	Thm*  A,B:Type. AB  Type
nat	Def   == {i:| 0i }
	Thm*    Type
one_one_corr_2	Def  A ~ B == f:(AB), g:(BA). InvFuns(A;B;f;g)
	Thm*  A,B:Type. (A ~ B)  Prop

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