The logical connective combining two statements, truth values, or formulas P and Q in such a way that the result is true only if both P and Q are false (see table). The NOR operation is the dual of the NAND operation (see duality). It may be represented by the Pierce arrow, ↓, or by ∇. P↓Q is just the negation of P∨Q, hence the name (see OR operation).
The NOR operation is of particular significance to computer designers since any Boolean expression can be expressed using the NOR operation alone. In practical terms, circuits can be built using only NOR gates.
NOR operation. Truth table