In mathematics, various typographical forms of brackets are frequently used in mathematical notation such as parentheses ( ), square brackets [ ], curly brackets { }, and angle brackets \langle\,\,\rangle. In the typical use, a mathematical expression is enclosed between an "opening bracket" and a matching "closing bracket". Generally such bracketing denotes some form of grouping: in evaluating an expression containing a bracketed subexpression, the operators in the subexpression take precedence over those surrounding it. Additionally, there are several specific uses and meanings for the various brackets.
Historically, other notations, such as the vinculum, were similarly used for grouping; in presentday use, these notations have all specific meanings. The earliest use of brackets to indicate aggregation (i.e. grouping) was suggested in 1608 by Christoforus Clavius and in 1629 by Albert Girard.^{[1]}
In the Z formal specification language, curly brackets denote a set and angle brackets denote a sequence.
Contents
 Symbols for representing angle brackets
 Algebra
 Functions
 Coordinates and vectors
 Intervals
 Sets and groups
 Matrices
 Derivatives
 Falling and rising factorial
 Quantum mechanics
 Lie bracket and commutator
 Floor / Ceiling functions and fractional part
 Highest common factor
 Notes
 See also

Symbols for representing angle brackets
A variety of different symbols are used to represent angle brackets. In email and other ASCII text it is common to use the lessthan () signs to represent angle brackets. Unicode has three pairs of dedicated characters:
 U+2329 ( ) and U+232A ( ) (left/rightpointing angle bracket) which are deprecated^{[2]}
 U+27E8 ( ) and U+27E9 ( ) (mathematical left/right angle bracket)
 U+3008 ( ) and U+3009 ( ) (left/right angle bracket in Chinese punctuation)
In LaTeX the markup is \langle and \rangle: \langle \,\, \rangle\,.
Algebra
In elementary algebra parentheses, ( ), are used to specify the order of operations, terms inside the bracket are evaluated first, hence 2 (3 + 4) is 14 and 10 5(1 + 0) is 2 and (2 3) + 4 is 10. This notation is extended to cover more general algebra involving variables: for example (x+y)\times(xy). Square brackets are also often used in place of a second set of parentheses when they are nested, to provide a visual distinction.
Also in mathematical expressions in general, parentheses are used to indicate grouping (that is, which parts belong together) when necessary to avoid ambiguities, or for the sake of clarity. For example, in the formula ( )_{X} = _{X} _{X}, used in the definition of composition of two natural transformations, the parentheses around serve to indicate that the indexing by X is applied to the composition , and not just its last component .
Functions
The arguments to a function are frequently surrounded by brackets: f(x) . It is common to omit the parentheses around the argument when there is little chance of ambiguity, thus: \sin x.
Coordinates and vectors
In the cartesian coordinate system brackets are used to specify the coordinates of a point: (2,3) denotes the point with xcoordinate 2 and ycoordinate 3.
The inner product of two vectors is commonly written as \langle a, b\rangle, but the notation (a, b) is also used.
Intervals
Both parentheses, ( ), and square brackets, [ ], can also be used to denote an interval. The notation [a, c) is used to indicate an interval from a to c that is inclusive of a but exclusive of c. That is, [5, 12) would be the set of all real numbers between 5 and 12, including 5 but not 12. The numbers may come as close as they like to 12, including 11.999 and so forth (with any finite number of 9s), but 12.0 is not included. In Europe, the notation [5,12[ is also used for this.
The endpoint adjoining the square bracket is known as closed, while the endpoint adjoining the parenthesis is known as open. If both types of brackets are the same, the entire interval may be referred to as closed or open as appropriate. Whenever infinity or negative infinity is used as an endpoint in the case of intervals on the real number line, it is always considered open and adjoined to a parenthesis. The endpoint can be closed when considering intervals on the extended real number line.
Sets and groups
Curly brackets { } are used to identify the elements of a set: {a,b,c} denotes a set of three elements.
Angle brackets are used in group theory to write group presentations, and to denote the subgroup generated by a collection of elements.
Matrices
An explicitly given matrix is commonly written between large round or square brackets:
 \begin{pmatrix} a & b \\ c & d \end{pmatrix} \quad\quad\begin{bmatrix} a & b \\ c & d \end{bmatrix}
Derivatives
The notation
 f^{(n)}(x)\,
stands for the nth derivative of function f, applied to argument x. So, for example, if f(x) = \exp(\lambda x), then f^{(n)}(x) = \lambda^n\exp(\lambda x). This is to be contrasted with f^n(x) = f(f(\ldots(f(x))\ldots)), the nfold application of f to argument x.
Falling and rising factorial
The notation (x)_{n} is used to denote the falling factorial, an nth degree polynomial defined by
 (x)_n=x(x1)(x2)\cdots(xn+1)=\frac{x!}{(xn)!}.
Confusingly, the same notation may be encountered as representing the rising factorial, also called "Pochhammer symbol". Another notation for the same is x^{(n)}. It can be defined by
 x^{(n)}=x(x+1)(x+2)\cdots(x+n1)=\frac{(x+n1)!}{(x1)!}.
Quantum mechanics
In quantum mechanics, angle brackets are also used as part of Dirac's formalism, braket notation, to note vectors from the dual spaces of the bra \left\langle A\right and the ket \leftB\right\rangle.
In statistical mechanics, angle brackets denote ensemble or time average.
Lie bracket and commutator
In group theory and ring theory, square brackets are used to denote the commutator. In group theory, the commutator [g,h] is commonly defined as g^{−1}h^{−1}gh. In ring theory, the commutator [a,b] is defined as ab − ba. Furthermore, in ring theory, braces are used to denote the anticommutator where {a,b} is defined as ab + ba.
The Lie bracket of a Lie algebra is a binary operation denoted by [\cdot,\cdot]:\mathfrak{g}\times\mathfrak{g}\to\mathfrak{g}. By using the commutator as a Lie bracket, every associative algebra can be turned into a Lie algebra. There are many different forms of Lie bracket, in particular the Lie derivative and the JacobiLie bracket.
Floor / Ceiling functions and fractional part
Square brackets, as in , are sometimes used to denote the floor function, which rounds a real number down to the next integer. However the floor and ceiling functions are usually typeset with left and right square brackets where the upper (for floor function) or lower (for ceiling function) horizontal bars are missing, as in \lfloor\pi\rfloor=3 or \lceil\pi\rceil=4.
Curly brackets, as in , may denote the fractional part of a real number.
Highest common factor
The notation (a, b) is sometimes used to denote the highest common factor of a and b. This may be extended to three or more arguments.
Notes

↑ Cajori, Florian 1980. A history of mathematics. New York: Chelsea Publishing, p. 158
 ↑
See also
 Iverson bracket
 Algebraic bracket
 Binomial coefficient
 Poisson bracket
 Bracket polynomial
 Pochhammer symbol
 Fr licherNijenhuis bracket
 NijenhuisRichardson bracket
 SchoutenNijenhuis bracket
 Dyck language
