Def Dec(P) == P  P

is mentioned by

Thm* b:. Dec(b)	[decidable__assert]
Thm* a,b:. Dec(a = b)	[decidable__equal_bool]

In prior sections: core int 1

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