Some definitions of interest.
decidable	Def Dec(P) == P  P
	Thm* A:Prop. Dec(A)  Prop
l_exists	Def (xL.P(x)) == x:T. (x  L) & P(x)
	Thm* T:Type, L:T List, P:(TProp). (xL.P(x))  Prop

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