Some definitions of interest.
lt_int	Def  i<j == if i<j true ; false fi
	Thm*  i,j:. (i<j)
nat	Def   == {i:| 0i }
	Thm*    Type

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