The term {tt (logior $tau_1 ldots tau_n$)} denotes the bit-wise logical inclusive or of the objects denoted by $tau_1$ through $tau_n$. It denotes 0 if there are no arguments.
(Undefined (Arity Logior))
(Instance-Of (Arity Logior) Undefined) (<- (Lognor ?X ?Y) (Lognot (Logior ?X ?Y))) (<- (Logorc1 ?X ?Y) (Logior (Lognot ?X) ?Y)) (<- (Logorc2 ?X ?Y) (Logior ?X (Lognot ?Y)))