# Definition:Logical NOR

## Definition

NOR (that is, not or), is a binary connective, written symbolically as $p \downarrow q$, whose behaviour is as follows:

$p \downarrow q$

is defined as:

neither $p$ nor $q$ is true.

$p \downarrow q$ is voiced:

$p$ nor $q$

The symbol $\downarrow$ is known as the Quine arrow, named after Willard Van Orman Quine.

### Truth Function

The NOR connective defines the truth function $f^\downarrow$ as follows:

 $\displaystyle f^\downarrow \left({F, F}\right)$ $=$ $\displaystyle T$ $\displaystyle f^\downarrow \left({F, T}\right)$ $=$ $\displaystyle F$ $\displaystyle f^\downarrow \left({T, F}\right)$ $=$ $\displaystyle F$ $\displaystyle f^\downarrow \left({T, T}\right)$ $=$ $\displaystyle F$

### Truth Table

The characteristic truth table of the logical NOR operator $p \downarrow q$ is as follows:

$\begin{array}{|cc||c|} \hline p & q & p \downarrow q \\ \hline F & F & T \\ F & T & F \\ T & F & F \\ T & T & F \\ \hline \end{array}$

### Boolean Interpretation

The truth value of $\mathbf A \downarrow \mathbf B$ under a boolean interpretation $v$ is given by:

$v \left({\mathbf A \downarrow \mathbf B}\right) = \begin{cases} T & : v \left({\mathbf A}\right) = v \left({\mathbf B}\right) = F\\ F & : \text{otherwise} \end{cases}$

## Notational Variants

Various symbols are encountered that denote the concept of logical NOR:

Symbol Origin Known as
$p \downarrow q$ Willard Quine Quine arrow
$p \ \mathsf{NOR} \ q$
$p \mathop \bot q$
$p \curlywedge q$ Charles Sanders Peirce Ampheck

The all-uppercase rendition NOR originates from the digital electronics industry, where, because NOR is Functionally Complete, this operator has a high importance.

## Also see

• Results about logical NOR can be found here.