Def  P  Q == P+Q

is mentioned by

Thm*  Q  Q  Q	[or_fused]
Thm*  P  Q  P  Q	[disjunct_elim]
Thm*  (P:Prop. P  P)  (P:Prop. P  P)	[negnegelim_vs_bivalence]
Def  P XOR Q == P  Q & (P & Q)	[xor]

In prior sections: core bool 1 rel 1

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