NAND  

Definition  
Truth table  
Logic gate  
Normal forms  
Disjunctive  
Conjunctive  
Zhegalkin polynomial  
Post's lattices  
0preserving  no 
1preserving  no 
Monotone  no 
Affine  no 
Logical connectives  



Related concepts  
Applications  
Category  
In Boolean functions and propositional calculus, the Sheffer stroke denotes a logical operation that is equivalent to the negation of the conjunction operation, expressed in ordinary language as "not both". It is also called nonconjunction, or alternative denial^{[1]} (since it says in effect that at least one of its operands is false), or NAND ("not and").^{[1]} In digital electronics, it corresponds to the NAND gate. It is named after Henry Maurice Sheffer and written as or as or as or as in Polish notation by Łukasiewicz (but not as , often used to represent disjunction).
Its dual is the NOR operator (also known as the Peirce arrow, Quine dagger or Webb operator). Like its dual, NAND can be used by itself, without any other logical operator, to constitute a logical formal system (making NAND functionally complete). This property makes the NAND gate crucial to modern digital electronics, including its use in computer processor design.
The nonconjunction is a logical operation on two logical values. It produces a value of true, if — and only if — at least one of the propositions is false.
The truth table of is as follows.
F  F  T 
F  T  T 
T  F  T 
T  T  F 
The Sheffer stroke of and is the negation of their conjunction
By De Morgan's laws, this is also equivalent to the disjunction of the negations of and
Peirce was the first to show the functional completeness of nonconjunction (representing this as ) but didn't publish his result.^{[2]}^{[3]} Peirce's editor added ) for nondisjunction^{[citation needed]}.^{[3]}
In 1911, Stamm was the first to publish a proof of the completeness of nonconjunction, representing this with (the Stamm hook)^{[4]} and nondisjunction in print at the first time and showed their functional completeness.^{[5]}
In 1913, Sheffer described nondisjunction using and showed its functional completeness. Sheffer also used for nondisjunction.^{[citation needed]} Many people, beginning with Nicod in 1917, and followed by Whitehead, Russell and many others, mistakenly thought Sheffer has described nonconjunction using , naming this the Sheffer Stroke.
In 1928, Hilbert and Ackermann described nonconjunction with the operator .^{[6]}^{[7]}
In 1929, Łukasiewicz used in for nonconjunction in his Polish notation.^{[8]}
An alternative notation for nonconjunction is . It is not clear who first introduced this notation, although the corresponding for nondisjunction was used by Quine in 1940,.^{[9]}
The stroke is named after Henry Maurice Sheffer, who in 1913 published a paper in the Transactions of the American Mathematical Society^{[10]} providing an axiomatization of Boolean algebras using the stroke, and proved its equivalence to a standard formulation thereof by Huntington employing the familiar operators of propositional logic (AND, OR, NOT). Because of selfduality of Boolean algebras, Sheffer's axioms are equally valid for either of the NAND or NOR operations in place of the stroke. Sheffer interpreted the stroke as a sign for nondisjunction (NOR) in his paper, mentioning nonconjunction only in a footnote and without a special sign for it. It was Jean Nicod who first used the stroke as a sign for nonconjunction (NAND) in a paper of 1917 and which has since become current practice.^{[11]}^{[12]} Russell and Whitehead used the Sheffer stroke in the 1927 second edition of Principia Mathematica and suggested it as a replacement for the "OR" and "NOT" operations of the first edition.
Charles Sanders Peirce (1880) had discovered the functional completeness of NAND or NOR more than 30 years earlier, using the term ampheck (for 'cutting both ways'), but he never published his finding. Two years before Sheffer, Edward Stamm also described the NAND and NOR operators and showed that the other Boolean operations could be expressed by it.^{[5]}
NAND does not possess any of the following five properties, each of which is required to be absent from, and the absence of all of which is sufficient for, at least one member of a set of functionally complete operators: truthpreservation, falsitypreservation, linearity, monotonicity, selfduality. (An operator is truth (or falsity)preserving if its value is truth (falsity) whenever all of its arguments are truth (falsity).) Therefore {NAND} is a functionally complete set.
This can also be realized as follows: All three elements of the functionally complete set {AND, OR, NOT} can be constructed using only NAND. Thus the set {NAND} must be functionally complete as well.
Expressed in terms of NAND , the usual operators of propositional logic are:


 


The Sheffer stroke, taken by itself, is a functionally complete set of connectives.^{[13]}^{[14]} This can be proved by first showing, with a truth table, that is truthfunctionally equivalent to .^{[15]} Then, since is truthfunctionally equivalent to ,^{[15]} and is equivalent to ,^{[15]} the Sheffer stroke suffices to define the set of connectives ,^{[15]} which is shown to be truthfunctionally complete by the Disjunctive Normal Form Theorem.^{[15]}