 Logical conjunction

"∧" redirects here. For exterior product, see exterior algebra.
In logic and mathematics, a twoplace logical operator and, also known as logical conjunction, results in true if both of its operands are true, otherwise the value of false.
The analogue of conjunction for a (possibly infinite) family of statements is universal quantification, which is part of predicate logic.
Contents
Notation
And is usually expressed with the prefix operator K, or an infix operator. In mathematics and logic, the infix operator is usually ∧; in electronics ; and in programming languages, & or and. Some programming languages have a related control structure, the shortcircuit and, written &&, and then, etc.
Definition
Logical conjunction is an operation on two logical values, typically the values of two propositions, that produces a value of true if and only if both of its operands are true.
Truth table
The truth table of :
INPUT OUTPUT A B A AND B 0 0 0 0 1 0 1 0 0 1 1 1 Introduction and elimination rules
As a rule of inference, conjunction introduction is a classically valid, simple argument form. The argument form has two premises, A and B. Intuitively, it permits the inference of their conjunction.
 A,
 B.
 Therefore, A and B.
or in logical operator notation:
 A,
 B
Here is an example of an argument that fits the form conjunction introduction:
 Bob likes apples.
 Bob likes oranges.
 Therefore, Bob likes apples and oranges.
Conjunction elimination is another classically valid, simple argument form. Intuitively, it permits the inference from any conjunction of either element of that conjunction.
 A and B.
 Therefore, A.
...or alternately,
 A and B.
 Therefore, B.
In logical operator notation:
...or alternately,
Properties
commutativity: yes
associativity: yes
distributivity: with various operations, especially with or
others with exclusive or:
with material nonimplication:
with itself:
idempotency: yes
monotonicity: yes
truthpreserving: yes
When all inputs are true, the output is true.(to be tested) falsehoodpreserving: yes
When all inputs are false, the output is false.(to be tested) Walsh spectrum: (1,1,1,1)
Nonlinearity: 1 (the function is bent)
If using binary values for true (1) and false (0), then logical conjunction works exactly like normal arithmetic multiplication.
Applications in computer engineering
In highlevel computer programming and digital electronics, logical conjunction is commonly represented by an infix operator, usually as a keyword such as "
AND
", an algebraic multiplication, or the ampersand symbol "&
". Many languages also provide shortcircuit control structures corresponding to logical conjunction.Logical conjunction is often used for bitwise operations, where
0
corresponds to false and1
to true:0 AND 0
=0
,0 AND 1
=0
,1 AND 0
=0
,1 AND 1
=1
.
The operation can also be applied to two binary words viewed as bitstrings of equal length, by taking the bitwise AND of each pair of bits at corresponding positions. For example:
11000110 AND 10100011
=10000010
.
This can be used to select part of a bitstring using a bit mask. For example,
10011101 AND 00001000
=00001000
extracts the fifth bit of an 8bit bitstring.In computer networking, bit masks are used to derive the network address of a subnet within an existing network from a given IP address, by ANDing the IP address and the subnet mask.
Logical conjunction "
AND
" is also used in SQL operations to form database queries.The CurryHoward correspondence relates logical conjunction to product types.
Settheoretic intersection
The intersection used in set theory is defined in terms of a logical conjunction: x ∈ A ∩ B if and only if (x ∈ A) ∧ (x ∈ B). Because of this, settheoretic intersection shares several properties with logical conjunction, such as associativity, commutativity, and idempotence.
Natural language
The logical conjunction and in logic is related to, but not the same as, the grammatical conjunction and in natural languages.
English "and" has properties not captured by logical conjunction. For example, "and" sometimes implies order. For example, "They got married and had a child" in common discourse means that the marriage came before the child. The word "and" can also imply a partition of a thing into parts, as "The American flag is red, white, and blue." Here it is not meant that the flag is at once red, white, and blue, but rather that it has a part of each color.
See also
 Andinverter graph
 AND gate
 Binary and
 Bitwise AND
 Boolean algebra (logic)
 Boolean algebra topics
 Boolean conjunctive query
 Boolean domain
 Boolean function
 Booleanvalued function
 Conjunction introduction
 Conjunction elimination
 De Morgan's laws
 Firstorder logic
 Grammatical conjunction
 Logical disjunction
 Logical negation
 Logical graph
 Logical value
 Operation
 PeanoRussell notation
 Propositional calculus
External links
Logical connectives Categories: Logical connectives
 Boolean algebra
 Binary operations
 Propositional calculus
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