Which expression represents the logical 'NOR' operation (P↓QP \downarrow QP↓Q)?
¬(P∧Q)\neg(P \land Q)¬(P∧Q)
¬(P∨Q)\neg(P \lor Q)¬(P∨Q)
¬P∨¬Q\neg P \lor \neg Q¬P∨¬Q
P∨QP \lor QP∨Q