Def x:A. B(x) == x:AB(x)

is mentioned by

Thm* E:(TTProp).  Thm* (x,y:T. Dec(E(x,y)))  (f:(TT). x,y:T. (x f y)  E(x,y))

[dec_iff_ex_bvfun]

In prior sections: core

Try larger context: StandardLIB IF YOU CAN SEE THIS go to /sfa/Nuprl/Shared/Xindentation_hack_doc.html