Logical NOR


In boolean logic, logical nor or joint denial is a truth-functional operator which produces a result that is the negation of logical or. That is, a sentence of the form is true precisely when neither p nor q is true—i.e. when both of p and q are false. In grammar, nor is a coordinating conjunction.
The NOR operator is also known as Peirce's arrow—Charles Sanders Peirce introduced the symbol ↓ for it, and demonstrated that the logical NOR is completely expressible: by combining uses of the logical NOR it is possible to express any logical operation on two variables. Thus, as with its dual, the NAND operator, NOR can be used by itself, without any other logical operator, to constitute a logical formal system. Other terms for the NOR operator include Quine's dagger, the by Peirce, and neither-nor.
Other ways of notating include, P NOR Q, and "Xpq".
It is logically equivalent to, where the symbol signifies OR and signifies the negation.
The computer used in the spacecraft that first carried humans to the moon, the Apollo Guidance Computer, was constructed entirely using NOR gates with three inputs.

Definition

The NOR operation is a logical operation on two logical values, typically the values of two propositions, that produces a value of true if and only if both operands are false. In other words, it produces a value of false if and only if at least one operand is true.

Truth table

The truth table of is as follows:
TTF
TFF
FTF
FFT

Logical Equivalences

The logical NOR is the negation of the disjunction:

Properties

Logical NOR does not possess any of the five qualities required to be absent from at least one member of a set of functionally complete operators. Thus, the set containing only NOR suffices as a complete set.

Other Boolean Operations in terms of the Logical NOR

NOR has the interesting feature that all other logical operators can be expressed by interlaced NOR operations.
The logical NAND operator also has this ability.
Expressed in terms of NOR, the usual operators of propositional logic are: