Def {a:T} == {x:T| x = a  T }

is mentioned by

Thm* Void =ext (x:. {x:})	[sfa_doc_void_via_isect2]
Thm* VoidA =ext {x.x:VoidA}	[sfa_doc_void_dom_fun_degenerate]
Thm* Void List =ext {nil:Void List}	[sfa_doc_void_list_is_singleton]
Thm* a:A, w:{a:A} List. z:A. z list w  z = a	[sfa_doc_inlist_singleton_const]

In prior sections: core

IF YOU CAN SEE THIS go to http://www.cs.cornell.edu/Info/People/sfa/Nuprl/Shared/Xindentation_hack_doc.html