Who Cites choose?
choose	Def @x:T. P(x) == InjCase(lem({x:T| P(x) }); x. x, arb(T))
	Thm* T:S, P:(TType). (@x:T. P(x))  T
arb	Def arb(T) == InjCase(lem(T); x. x, "uu")
	Thm* T:S. arb(T)  T

Syntax:

@x:T. P(x)

has structure:

choose(T; x.P(x))

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