Contents

Glossary of mathematical symbols

The most basic symbols are the decimal digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9), and the letters of the Latin alphabet. The decimal digits are used for representing numbers through the Hindu–Arabic numeral system. Historically, upper-case letters were used for representing points in geometry, and lower-case letters were used for variables and constants. Letters are used for representing many other sorts of mathematical objects. As the number of these sorts has remarkably increased in modern mathematics, the Greek alphabet and some Hebrew letters are also used. In mathematical formulas, the standard typefaceisitalic type for Latin letters and lower-case Greek letters, and upright type for upper case Greek letters. For having more symbols, other typefaces are also used, mainly boldface ${\displaystyle \mathbf {a,A,b,B} ,\ldots }$, script typeface ${\displaystyle {\mathcal {A,B}},\ldots }$ (the lower-case script face is rarely used because of the possible confusion with the standard face), German fraktur ${\displaystyle {\mathfrak {a,A,b,B}},\ldots }$, and blackboard bold ${\displaystyle \mathbb {N,Z,Q,R,C,H,F} _{q}}$ (the other letters are rarely used in this face, or their use is unconventional).

The use of Latin and Greek letters as symbols for denoting mathematical objects is not described in this article. For such uses, see Variable (mathematics) and List of mathematical constants. However, some symbols that are described here have the same shape as the letter from which they are derived, such as ${\displaystyle \textstyle \prod {}}$ and ${\displaystyle \textstyle \sum {}}$.

These letters alone are not sufficient for the needs of mathematicians, and many other symbols are used. Some take their origin in punctuation marks and diacritics traditionally used in typography; others by deforming letter forms, as in the cases of ${\displaystyle \in }$ and ${\displaystyle \forall }$. Others, such as + and =, were specially designed for mathematics.

Layout of this article[edit]

Normally, entries of a glossary are structured by topics and sorted alphabetically. This is not possible here, as there is no natural order on symbols, and many symbols are used in different parts of mathematics with different meanings, often completely unrelated. Therefore, some arbitrary choices had to be made, which are summarized below.

The article is split into sections that are sorted by an increasing level of technicality. That is, the first sections contain the symbols that are encountered in most mathematical texts, and that are supposed to be known even by beginners. On the other hand, the last sections contain symbols that are specific to some area of mathematics and are ignored outside these areas. However, the long section on brackets has been placed near to the end, although most of its entries are elementary: this makes it easier to search for a symbol entry by scrolling.

Most symbols have multiple meanings that are generally distinguished either by the area of mathematics where they are used or by their syntax, that is, by their position inside a formula and the nature of the other parts of the formula that are close to them.

As readers may not be aware of the area of mathematics to which the symbol that they are looking for is related, the different meanings of a symbol are grouped in the section corresponding to their most common meaning.

When the meaning depends on the syntax, a symbol may have different entries depending on the syntax. For summarizing the syntax in the entry name, the symbol ${\displaystyle \Box }$ is used for representing the neighboring parts of a formula that contains the symbol. See § Brackets for examples of use.

Most symbols have two printed versions. They can be displayed as Unicode characters, or in LaTeX format. With the Unicode version, using search engines and copy-pasting are easier. On the other hand, the LaTeX rendering is often much better (more aesthetic), and is generally considered a standard in mathematics. Therefore, in this article, the Unicode version of the symbols is used (when possible) for labelling their entry, and the LaTeX version is used in their description. So, for finding how to type a symbol in LaTeX, it suffices to look at the source of the article.

For most symbols, the entry name is the corresponding Unicode symbol. So, for searching the entry of a symbol, it suffices to type or copy the Unicode symbol into the search textbox. Similarly, when possible, the entry name of a symbol is also an anchor, which allows linking easily from another Wikipedia article. When an entry name contains special characters such as [, ], and |, there is also an anchor, but one has to look at the article source to know it.

Finally, when there is an article on the symbol itself (not its mathematical meaning), it is linked to in the entry name.

Arithmetic operators[edit]

+    (plus sign)

1.  Denotes addition and is read as plus; for example, 3 + 2.

2.  Denotes that a number is positive and is read as plus. Redundant, but sometimes used for emphasizing that a number is positive, specially when other numbers in the context are or may be negative; for example, +2.

3.  Sometimes used instead of ${\displaystyle \sqcup }$ for a disjoint unionofsets.

-    (minus sign)

1.  Denotes subtraction and is read as minus; for example, 3 – 2.

2.  Denotes the additive inverse and is read as negativeorthe opposite of; for example, –2.

3.  Also used in place of \ for denoting the set-theoretic complement; see \in§ Set theory.

×    (multiplication sign)

1.  Inelementary arithmetic, denotes multiplication, and is read as times; for example, 3 × 2.

2.  Ingeometry and linear algebra, denotes the cross product.

3.  Inset theory and category theory, denotes the Cartesian product and the direct product. See also ×in§ Set theory.

·    (dot)

1.  Denotes multiplication and is read as times; for example, 3 ⋅ 2.

2.  Ingeometry and linear algebra, denotes the dot product.

3.  Placeholder used for replacing an indeterminate element. For example, saying "the absolute value is denoted by | · |" is perhaps clearer than saying that it is denoted as | |.

±    (plus–minus sign)

1.  Denotes either a plus sign or a minus sign.

2.  Denotes the range of values that a measured quantity may have; for example, 10 ± 2 denotes an unknown value that lies between 8 and 12.

∓    (minus-plus sign)

Used paired with ±, denotes the opposite sign; that is, +if±is–, and –if±is+.

÷    (division sign)

Widely used for denoting divisionin Anglophone countries, it is no longer in common use in mathematics and its use is "not recommended".^[1] In some countries, it can indicate subtraction.

:    (colon)

1.  Denotes the ratio of two quantities.

2.  In some countries, may denote division.

3.  Inset-builder notation, it is used as a separator meaning "such that"; see {□ : □}.

/    (slash)

1.  Denotes division and is read as divided byorover. Often replaced by a horizontal bar. For example, 3 / 2or${\displaystyle {\frac {3}{2}}}$.

2.  Denotes a quotient structure. For example, quotient set, quotient group, quotient category, etc.

3.  Innumber theory and field theory, ${\displaystyle F/E}$ denotes a field extension, where F is an extension field of the field E.

4.  Inprobability theory, denotes a conditional probability. For example, ${\displaystyle P(A/B)}$ denotes the probability of A, given that B occurs. Also denoted ${\displaystyle P(A\mid B)}$: see "|".

√    (square-root symbol)

Denotes square root and is read as the square root of. Rarely used in modern mathematics without a horizontal bar delimiting the width of its argument (see the next item). For example, √2.

√     (radical symbol)

1.  Denotes square root and is read as the square root of. For example, ${\displaystyle {\sqrt {3+2}}}$.

2.  With an integer greater than 2 as a left superscript, denotes an nth root. For example, ${\displaystyle {\sqrt[{7}]{3}}}$ denotes the 7th root of 3.

^    (caret)

1.  Exponentiation is normally denoted with a superscript. However, ${\displaystyle x^{y}}$ is often denoted x^y when superscripts are not easily available, such as in programming languages (including LaTeX) or plain text emails.

2.  Not to be confused with ∧

Equality, equivalence and similarity[edit]

=    (equals sign)

1.  Denotes equality.

2.  Used for naming a mathematical object in a sentence like "let ${\displaystyle x=E}$ ", where E is an expression. See also ≝, ≜ or${\displaystyle :=}$.

${\displaystyle \triangleq \quad {\stackrel {\scriptscriptstyle \mathrm {def} }{=}}\quad :=}$

Any of these is sometimes used for naming a mathematical object. Thus, ${\displaystyle x\triangleq E,}$ ${\displaystyle x\mathrel {\stackrel {\scriptscriptstyle \mathrm {def} }{=}} E,}$ ${\displaystyle x\mathrel {:=} E}$ and ${\displaystyle E\mathrel {=:} x}$ are each an abbreviation of the phrase "let ${\displaystyle x=E}$", where ${\displaystyle E}$ is an expression and ${\displaystyle x}$ is a variable. This is similar to the concept of assignment in computer science, which is variously denoted (depending on the programming language used) ${\displaystyle =,:=,\leftarrow ,\ldots }$

≠    (not-equal sign)

Denotes inequality and means "not equal".

≈

The most common symbol for denoting approximate equality. For example, ${\displaystyle \pi \approx 3.14159.}$

~    (tilde)

1.  Between two numbers, either it is used instead of ≈ to mean "approximatively equal", or it means "has the same order of magnitude as".

2.  Denotes the asymptotic equivalence of two functions or sequences.

3.  Often used for denoting other types of similarity, for example, matrix similarityorsimilarity of geometric shapes.

4.  Standard notation for an equivalence relation.

5.  Inprobability and statistics, may specify the probability distribution of a random variable. For example, ${\displaystyle X\sim N(0,1)}$ means that the distribution of the random variable Xisstandard normal.^[2]

6.  Notation for proportionality. See also ∝ for a less ambiguous symbol.

≡    (triple bar)

1.  Denotes an identity, that is, an equality that is true whichever values are given to the variables occurring in it.

2.  Innumber theory, and more specifically in modular arithmetic, denotes the congruence modulo an integer.

3.  May denote a logical equivalence.

${\displaystyle \cong }$

1.  May denote an isomorphism between two mathematical structures, and is read as "is isomorphic to".

2.  Ingeometry, may denote the congruence of two geometric shapes (that is the equality up toadisplacement), and is read "is congruent to".

Comparison[edit]

<    (less-than sign)

1.  Strict inequality between two numbers; means and is read as "less than".

2.  Commonly used for denoting any strict order.

3.  Between two groups, may mean that the first one is a proper subgroup of the second one.

>    (greater-than sign)

1.  Strict inequality between two numbers; means and is read as "greater than".

2.  Commonly used for denoting any strict order.

3.  Between two groups, may mean that the second one is a proper subgroup of the first one.

≤

1.  Means "less than or equal to". That is, whatever A and B are, A ≤ B is equivalent to A < BorA = B.

2.  Between two groups, may mean that the first one is a subgroup of the second one.

≥

1.  Means "greater than or equal to". That is, whatever A and B are, A ≥ B is equivalent to A > BorA = B.

2.  Between two groups, may mean that the second one is a subgroup of the first one.

${\displaystyle \ll {\text{ and }}\gg }$

1.  Means "much less than" and "much greater than". Generally, much is not formally defined, but means that the lesser quantity can be neglected with respect to the other. This is generally the case when the lesser quantity is smaller than the other by one or several orders of magnitude.

2.  Inmeasure theory, ${\displaystyle \mu \ll \nu }$ means that the measure ${\displaystyle \mu }$ is absolutely continuous with respect to the measure ${\displaystyle \nu }$.

${\displaystyle \leqq }$

A rarely used symbol, generally a synonym of ≤.

${\displaystyle \prec {\text{ and }}\succ }$

1.  Often used for denoting an order or, more generally, a preorder, when it would be confusing or not convenient to use < and >.

2.  Sequentioninasynchronous logic.

Set theory[edit]

∅

Denotes the empty set, and is more often written ${\displaystyle \emptyset }$. Using set-builder notation, it may also be denoted ${\displaystyle \{\}}$.

#    (number sign)

1.  Number of elements: ${\displaystyle \#{}S}$ may denote the cardinality of the set S. An alternative notation is ${\displaystyle |S|}$; see ${\displaystyle |\square |}$.

2.  Primorial: ${\displaystyle n{}\#}$ denotes the product of the prime numbers that are not greater than n.

3.  Intopology, ${\displaystyle M\#N}$ denotes the connected sum of two manifolds or two knots.

∈

Denotes set membership, and is read "is in" or "belongs to". That is, ${\displaystyle x\in S}$ means that x is an element of the set S.

∉

Means "is not in". That is, ${\displaystyle x\notin S}$ means ${\displaystyle \neg (x\in S)}$.

⊂

Denotes set inclusion. However two slightly different definitions are common.

1.  ${\displaystyle A\subset B}$ may mean that A is a subsetofB, and is possibly equal to B; that is, every element of A belongs to B; in formula, ${\displaystyle \forall {}x,\,x\in A\Rightarrow x\in B}$.

2.  ${\displaystyle A\subset B}$ may mean that A is a proper subsetofB, that is the two sets are different, and every element of A belongs to B; in formula, ${\displaystyle A\neq B\land \forall {}x,\,x\in A\Rightarrow x\in B}$.

⊆

${\displaystyle A\subseteq B}$ means that A is a subsetofB. Used for emphasizing that equality is possible, or when ${\displaystyle A\subset B}$ means that ${\displaystyle A}$ is a proper subset of ${\displaystyle B.}$

⊊

${\displaystyle A\subsetneq B}$ means that A is a proper subsetofB. Used for emphasizing that ${\displaystyle A\neq B}$, or when ${\displaystyle A\subset B}$ does not imply that ${\displaystyle A}$ is a proper subset of ${\displaystyle B.}$

⊃, ⊇, ⊋

Denote the converse relation of ${\displaystyle \subset }$, ${\displaystyle \subseteq }$, and ${\displaystyle \subsetneq }$ respectively. For example, ${\displaystyle B\supset A}$ is equivalent to ${\displaystyle A\subset B}$.

∪

Denotes set-theoretic union, that is, ${\displaystyle A\cup B}$ is the set formed by the elements of A and B together. That is, ${\displaystyle A\cup B=\{x\mid (x\in A)\lor (x\in B)\}}$.

∩

Denotes set-theoretic intersection, that is, ${\displaystyle A\cap B}$ is the set formed by the elements of both A and B. That is, ${\displaystyle A\cap B=\{x\mid (x\in A)\land (x\in B)\}}$.

∖    (backslash)

Set difference; that is, ${\displaystyle A\setminus B}$ is the set formed by the elements of A that are not in B. Sometimes, ${\displaystyle A-B}$ is used instead; see –in§ Arithmetic operators.

⊖or${\displaystyle \triangle }$

Symmetric difference: that is, ${\displaystyle A\ominus B}$or${\displaystyle A\operatorname {\triangle } B}$ is the set formed by the elements that belong to exactly one of the two sets A and B.

${\displaystyle \complement }$

1.  With a subscript, denotes a set complement: that is, if ${\displaystyle B\subseteq A}$, then ${\displaystyle \complement _{A}B=A\setminus B}$.

2.  Without a subscript, denotes the absolute complement; that is, ${\displaystyle \complement A=\complement _{U}A}$, where U is a set implicitly defined by the context, which contains all sets under consideration. This set U is sometimes called the universe of discourse.

×    (multiplication sign)

See also ×in§ Arithmetic operators.

1.  Denotes the Cartesian product of two sets. That is, ${\displaystyle A\times B}$ is the set formed by all pairs of an element of A and an element of B.

2.  Denotes the direct product of two mathematical structures of the same type, which is the Cartesian product of the underlying sets, equipped with a structure of the same type. For example, direct product of rings, direct product of topological spaces.

3.  Incategory theory, denotes the direct product (often called simply product) of two objects, which is a generalization of the preceding concepts of product.

${\displaystyle \sqcup }$

Denotes the disjoint union. That is, if A and B are sets then ${\displaystyle A\sqcup B=\left(A\times \{i_{A}\}\right)\cup \left(B\times \{i_{B}\}\right)}$ is a set of pairs where i_A and i_B are distinct indices discriminating the members of A and BinFailed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "http://localhost:6011/en.wikipedia.org/v1/":): {\displaystyle A\sqcup B} .

${\displaystyle \bigsqcup {\text{ or }}\coprod }$

1.  Used for the disjoint union of a family of sets, such as in ${\textstyle \bigsqcup _{i\in I}A_{i}.}$

2.  Denotes the coproductofmathematical structures or of objects in a category.

Basic logic[edit]

Several logical symbols are widely used in all mathematics, and are listed here. For symbols that are used only in mathematical logic, or are rarely used, see List of logic symbols.

¬    (not sign)

Denotes logical negation, and is read as "not". If E is a logical predicate, ${\displaystyle \neg E}$ is the predicate that evaluates to true if and only if E evaluates to false. For clarity, it is often replaced by the word "not". In programming languages and some mathematical texts, it is sometimes replaced by "~" or "!", which are easier to type on some keyboards.

∨    (descending wedge)

1.  Denotes the logical or, and is read as "or". If E and F are logical predicates, ${\displaystyle E\lor F}$ is true if either E, F, or both are true. It is often replaced by the word "or".

2.  Inlattice theory, denotes the joinorleast upper bound operation.

3.  Intopology, denotes the wedge sum of two pointed spaces.

∧    (wedge)

1.  Denotes the logical and, and is read as "and". If E and F are logical predicates, ${\displaystyle E\land F}$ is true if E and F are both true. It is often replaced by the word "and" or the symbol "&".

2.  Inlattice theory, denotes the meetorgreatest lower bound operation.

3.  Inmultilinear algebra, geometry, and multivariable calculus, denotes the wedge product or the exterior product.

⊻

Exclusive or: if E and F are two Boolean variablesorpredicates, ${\displaystyle E\veebar F}$ denotes the exclusive or. Notations E XOR F and ${\displaystyle E\oplus F}$ are also commonly used; see ⊕.

∀    (turned A)

1.  Denotes universal quantification and is read as "for all". If E is a logical predicate, ${\displaystyle \forall xE}$ means that E is true for all possible values of the variable x.

2.  Often used improperly^[3] in plain text as an abbreviation of "for all" or "for every".

∃

1.  Denotes existential quantification and is read "there exists ... such that". If E is a logical predicate, ${\displaystyle \exists xE}$ means that there exists at least one value of x for which E is true.

2.  Often used improperly^[3] in plain text as an abbreviation of "there exists".

∃!

Denotes uniqueness quantification, that is, ${\displaystyle \exists !xP}$ means "there exists exactly one x such that P (is true)". In other words, ${\displaystyle \exists !xP($x)} is an abbreviation of ${\displaystyle \exists x\,(P($x)\,\wedge \neg \exists y\,(P(y)\wedge y\neq x))} .

⇒

1.  Denotes material conditional, and is read as "implies". If P and Q are logical predicates, ${\displaystyle P\Rightarrow Q}$ means that if P is true, then Q is also true. Thus, ${\displaystyle P\Rightarrow Q}$ is logically equivalent with ${\displaystyle Q\lor \neg P}$.

2.  Often used improperly^[3] in plain text as an abbreviation of "implies".

⇔

1.  Denotes logical equivalence, and is read "is equivalent to" or "if and only if". If P and Q are logical predicates, ${\displaystyle P\Leftrightarrow Q}$ is thus an abbreviation of ${\displaystyle (P\Rightarrow Q)\land (Q\Rightarrow P)}$, or of ${\displaystyle (P\land Q)\lor (\neg P\land \neg Q)}$.

2.  Often used improperly^[3] in plain text as an abbreviation of "if and only if".

⊤    (Tee)

1.  ${\displaystyle \top }$ denotes the logical predicate always true.

2.  Denotes also the truth value true.

3.  Sometimes denotes the top element of a bounded lattice (previous meanings are specific examples).

4.  For the use as a superscript, see □^⊤.

⊥    (Up tack)

1.  ${\displaystyle \bot }$ denotes the logical predicate always false.

2.  Denotes also the truth value false.

3.  Sometimes denotes the bottom element of a bounded lattice (previous meanings are specific examples).

4.  InCryptography often denotes an error in place of a regular value.

5.  For the use as a superscript, see □^⊥.

6.  For the similar symbol, see ${\displaystyle \perp }$.

Blackboard bold[edit]

The blackboard bold typeface is widely used for denoting the basic number systems. These systems are often also denoted by the corresponding uppercase bold letter. A clear advantage of blackboard bold is that these symbols cannot be confused with anything else. This allows using them in any area of mathematics, without having to recall their definition. For example, if one encounters ${\displaystyle \mathbb {R} }$incombinatorics, one should immediately know that this denotes the real numbers, although combinatorics does not study the real numbers (but it uses them for many proofs).

${\displaystyle \mathbb {N} }$

Denotes the set of natural numbers ${\displaystyle \{1,2,\ldots \},}$ or sometimes ${\displaystyle \{0,1,2,\ldots \}.}$ When the distinction is important and readers might assume either definition, ${\displaystyle \mathbb {N} _{1}}$ and ${\displaystyle \mathbb {N} _{0}}$ are used, respectively, to denote one of them unambiguously. Notation ${\displaystyle \mathbf {N} }$ is also commonly used.

${\displaystyle \mathbb {Z} }$

Denotes the set of integers ${\displaystyle \{\ldots ,-2,-1,0,1,2,\ldots \}.}$ It is often denoted also by ${\displaystyle \mathbf {Z} .}$

${\displaystyle \mathbb {Z} _{p}}$

1.  Denotes the set of p-adic integers, where p is a prime number.

2.  Sometimes, ${\displaystyle \mathbb {Z} _{n}}$ denotes the integers modulo n, where n is an integer greater than 0. The notation ${\displaystyle \mathbb {Z} /n\mathbb {Z} }$ is also used, and is less ambiguous.

${\displaystyle \mathbb {Q} }$

Denotes the set of rational numbers (fractions of two integers). It is often denoted also by ${\displaystyle \mathbf {Q} .}$

${\displaystyle \mathbb {Q} _{p}}$

Denotes the set of p-adic numbers, where p is a prime number.

${\displaystyle \mathbb {R} }$

Denotes the set of real numbers. It is often denoted also by ${\displaystyle \mathbf {R} .}$

${\displaystyle \mathbb {C} }$

Denotes the set of complex numbers. It is often denoted also by ${\displaystyle \mathbf {C} .}$

${\displaystyle \mathbb {H} }$

Denotes the set of quaternions. It is often denoted also by ${\displaystyle \mathbf {H} .}$

${\displaystyle \mathbb {F} _{q}}$

Denotes the finite field with q elements, where q is a prime power (including prime numbers). It is denoted also by GF(q).

${\displaystyle \mathbb {O} }$

Used on rare occasions to denote the set of octonions. It is often denoted also by ${\displaystyle \mathbf {O} .}$

Calculus[edit]

□'

Lagrange's notation for the derivative: If f is a function of a single variable, ${\displaystyle f'}$, read as "f prime", is the derivative of f with respect to this variable. The second derivative is the derivative of ${\displaystyle f'}$, and is denoted ${\displaystyle f''}$.

${\displaystyle {\dot {\Box }}}$

Newton's notation, most commonly used for the derivative with respect to time: If x is a variable depending on time, then ${\displaystyle {\dot {x}}}$ is its derivative with respect to time. In particular, if x represents a moving point, then ${\displaystyle {\dot {x}}}$ is its velocity.

${\displaystyle {\ddot {\Box }}}$

Newton's notation, for the second derivative: If x is a variable that represents a moving point, then ${\displaystyle {\ddot {x}}}$ is its acceleration.

d □/d □

Leibniz's notation for the derivative, which is used in several slightly different ways.

1.  Ify is a variable that dependsonx, then ${\displaystyle \textstyle {\frac {\mathrm {d} y}{\mathrm {d} x}}}$, read as "d y over d x", is the derivative of y with respect to x.

2.  Iff is a function of a single variable x, then ${\displaystyle \textstyle {\frac {\mathrm {d} f}{\mathrm {d} x}}}$ is the derivative of f, and ${\displaystyle \textstyle {\frac {\mathrm {d} f}{\mathrm {d} x}}($a)} is the value of the derivative at a.

3.  Total derivative: If ${\displaystyle f(x_{1},\ldots ,x_{n})}$ is a function of several variables that dependonx, then ${\displaystyle \textstyle {\frac {\mathrm {d} f}{\mathrm {d} x}}}$ is the derivative of f considered as a function of x. That is, ${\displaystyle \textstyle {\frac {\mathrm {d} f}{dx}}=\sum _{i=1}^{n}{\frac {\partial f}{\partial x_{i}}}\,{\frac {\mathrm {d} x_{i}}{\mathrm {d} x}}}$.

∂ □/∂ □

Partial derivative: If ${\displaystyle f(x_{1},\ldots ,x_{n})}$ is a function of several variables, ${\displaystyle \textstyle {\frac {\partial f}{\partial x_{i}}}}$ is the derivative with respect to the ith variable considered as an independent variable, the other variables being considered as constants.

𝛿 □/𝛿 □

Functional derivative: If ${\displaystyle f(y_{1},\ldots ,y_{n})}$ is a functional of several functions, ${\displaystyle \textstyle {\frac {\delta f}{\delta y_{i}}}}$ is the functional derivative with respect to the nth function considered as an independent variable, the other functions being considered constant.

${\displaystyle {\overline {\Box }}}$

1.  Complex conjugate: If z is a complex number, then ${\displaystyle {\overline {z}}}$ is its complex conjugate. For example, ${\displaystyle {\overline {a+bi}}=a-bi}$.

2.  Topological closure: If S is a subset of a topological space T, then ${\displaystyle {\overline {S}}}$ is its topological closure, that is, the smallest closed subsetofT that contains S.

3.  Algebraic closure: If F is a field, then ${\displaystyle {\overline {F}}}$ is its algebraic closure, that is, the smallest algebraically closed field that contains F. For example, ${\displaystyle {\overline {\mathbb {Q} }}}$ is the field of all algebraic numbers.

4.  Mean value: If x is a variable that takes its values in some sequence of numbers S, then ${\displaystyle {\overline {x}}}$ may denote the mean of the elements of S.

→

1.  ${\displaystyle A\to B}$ denotes a function with domain A and codomain B. For naming such a function, one writes ${\displaystyle f:A\to B}$, which is read as "f from AtoB".

2.  More generally, ${\displaystyle A\to B}$ denotes a homomorphism or a morphism from AtoB.

3.  May denote a logical implication. For the material implication that is widely used in mathematics reasoning, it is nowadays generally replaced by ⇒. In mathematical logic, it remains used for denoting implication, but its exact meaning depends on the specific theory that is studied.

4.  Over a variable name, means that the variable represents a vector, in a context where ordinary variables represent scalars; for example, ${\displaystyle {\overrightarrow {v}}}$. Boldface (${\displaystyle \mathbf {v} }$) or a circumflex (${\displaystyle {\hat {v}}}$) are often used for the same purpose.

5.  InEuclidean geometry and more generally in affine geometry, ${\displaystyle {\overrightarrow {PQ}}}$ denotes the vector defined by the two points P and Q, which can be identified with the translation that maps PtoQ. The same vector can be denoted also ${\displaystyle Q-P}$; see Affine space.

↦

Used for defining a function without having to name it. For example, ${\displaystyle x\mapsto x^{2}}$ is the square function.

○^[4]

1.  Function composition: If f and g are two functions, then ${\displaystyle g\circ f}$ is the function such that ${\displaystyle (g\circ f)($x)=g(f(x))} for every value of x.

2.  Hadamard product of matrices: If A and B are two matrices of the same size, then ${\displaystyle A\circ B}$ is the matrix such that ${\displaystyle (A\circ B)_{i,j}=($A)_{i,j}(B)_{i,j}} . Possibly, ${\displaystyle \circ }$ is also used instead of ⊙ for the Hadamard product of power series.^{[citation needed]}

∂

1.  Boundary of a topological subspace: If S is a subspace of a topological space, then its boundary, denoted ${\displaystyle \partial S}$, is the set difference between the closure and the interiorofS.

2.  Partial derivative: see ∂□/∂□.

∫

1.  Without a subscript, denotes an antiderivative. For example, ${\displaystyle \textstyle \int x^{2}dx={\frac {x^{3}}{3}}+C}$.

2.  With a subscript and a superscript, or expressions placed below and above it, denotes a definite integral. For example, ${\displaystyle \textstyle \int _{a}^{b}x^{2}dx={\frac {b^{3}-a^{3}}{3}}}$.

3.  With a subscript that denotes a curve, denotes a line integral. For example, ${\displaystyle \textstyle \int _{C}f=\int _{a}^{b}f(r($t))r'(t)\operatorname {d} t} , if r is a parametrization of the curve C, from atob.

∮

Often used, typically in physics, instead of ${\displaystyle \textstyle \int }$ for line integrals over a closed curve.

∬, ∯

Similar to ${\displaystyle \textstyle \int }$ and ${\displaystyle \textstyle \oint }$ for surface integrals.

${\displaystyle {\boldsymbol {\nabla }}}$or${\displaystyle {\vec {\nabla }}}$

Nabla, the gradient or vector derivative operator ${\displaystyle \textstyle \left({\frac {\partial }{\partial x}},{\frac {\partial }{\partial y}},{\frac {\partial }{\partial z}}\right)}$, also called delorgrad.

∇²or∇⋅∇

Laplace operatororLaplacian: ${\displaystyle \textstyle {\frac {\partial ^{2}}{\partial x^{2}}}+{\frac {\partial ^{2}}{\partial y^{2}}}+{\frac {\partial ^{2}}{\partial z^{2}}}}$. The forms ${\displaystyle \nabla ^{2}}$ and ${\displaystyle {\boldsymbol {\nabla }}\cdot {\boldsymbol {\nabla }}}$ represent the dot product of the gradient (${\displaystyle {\boldsymbol {\nabla }}}$or${\displaystyle {\vec {\nabla }}}$) with itself. Also notated Δ (next item).

Δ

(Capital Greek letter delta—not to be confused with ${\displaystyle \triangle }$, which may denote a geometric triangle or, alternatively, the symmetric difference of two sets.)

1.  Another notation for the Laplacian (see above).

2.  Operator of finite difference.

${\displaystyle {\boldsymbol {\partial }}}$or${\displaystyle \partial _{\mu }}$

(Note: the notation ${\displaystyle \Box }$ is not recommended for the four-gradient since both ${\displaystyle \Box }$ and ${\displaystyle {\Box }^{2}}$ are used to denote the d'Alembertian; see below.)

Quad, the 4-vector gradient operatororfour-gradient, ${\displaystyle \textstyle \left({\frac {\partial }{\partial t}},{\frac {\partial }{\partial x}},{\frac {\partial }{\partial y}},{\frac {\partial }{\partial z}}\right)}$.

${\displaystyle \Box }$or${\displaystyle {\Box }^{2}}$

(here an actual box, not a placeholder)

Denotes the d'Alembertian or squared four-gradient, which is a generalization of the Laplacian to four-dimensional spacetime. In flat spacetime with Euclidean coordinates, this may mean either ${\displaystyle ~\textstyle -{\frac {\partial ^{2}}{\partial t^{2}}}+{\frac {\partial ^{2}}{\partial x^{2}}}+{\frac {\partial ^{2}}{\partial y^{2}}}+{\frac {\partial ^{2}}{\partial z^{2}}}~\;}$or${\displaystyle \;~\textstyle +{\frac {\partial ^{2}}{\partial t^{2}}}-{\frac {\partial ^{2}}{\partial x^{2}}}-{\frac {\partial ^{2}}{\partial y^{2}}}-{\frac {\partial ^{2}}{\partial z^{2}}}~\;}$; the sign convention must be specified. In curved spacetime (or flat spacetime with non-Euclidean coordinates), the definition is more complicated. Also called boxorquabla.

Linear and multilinear algebra[edit]

∑    (Sigma notation)

1.  Denotes the sum of a finite number of terms, which are determined by subscripts and superscripts (which can also be placed below and above), such as in ${\displaystyle \textstyle \sum _{i=1}^{n}i^{2}}$or${\displaystyle \textstyle \sum _{0<i<j<n}j-i}$.

2.  Denotes a series and, if the series is convergent, the sum of the series. For example, ${\displaystyle \textstyle \sum _{i=0}^{\infty }{\frac {x^{i}}{i!}}=e^{x}}$.

∏    (Capital-pi notation)

1.  Denotes the product of a finite number of terms, which are determined by subscripts and superscripts (which can also be placed below and above), such as in ${\displaystyle \textstyle \prod _{i=1}^{n}i^{2}}$or${\displaystyle \textstyle \prod _{0<i<j<n}j-i}$.

2.  Denotes an infinite product. For example, the Euler product formula for the Riemann zeta functionis${\displaystyle \textstyle \zeta ($z)=\prod _{n=1}^{\infty }{\frac {1}{1-p_{n}^{-z}}}} .

3.  Also used for the Cartesian product of any number of sets and the direct product of any number of mathematical structures.

${\displaystyle \oplus }$    (circled plus)

1.  Internal direct sum: if E and F are abelian subgroups of an abelian group V, notation ${\displaystyle V=E\oplus F}$ means that V is the direct sum of E and F; that is, every element of V can be written in a unique way as the sum of an element of E and an element of F. This applies also when E and F are linear subspacesorsubmodules of the vector spaceormodule V.

2.  Direct sum: if E and F are two abelian groups, vector spaces, or modules, then their direct sum, denoted ${\displaystyle E\oplus F}$ is an abelian group, vector space, or module (respectively) equipped with two monomorphisms ${\displaystyle f:E\to E\oplus F}$ and ${\displaystyle g:F\to E\oplus F}$ such that ${\displaystyle E\oplus F}$ is the internal direct sum of ${\displaystyle f($E)} and ${\displaystyle g($F)} . This definition makes sense because this direct sum is unique up to a unique isomorphism.

3.  Exclusive or: if E and F are two Boolean variablesorpredicates, ${\displaystyle E\oplus F}$ may denote the exclusive or. Notations E XOR F and ${\displaystyle E\veebar F}$ are also commonly used; see ⊻.

⊗

1.  Denotes the tensor productofabelian groups, vector spaces, modules, or other mathematical structures, such as in ${\displaystyle E\otimes F,}$or${\displaystyle E\otimes _{K}F.}$

2.  Denotes the tensor product of elements: if ${\displaystyle x\in E}$ and ${\displaystyle y\in F,}$ then ${\displaystyle x\otimes y\in E\otimes F.}$

□^⊤

1.  Transpose: if A is a matrix, ${\displaystyle A^{\top }}$ denotes the transposeofA, that is, the matrix obtained by exchanging rows and columns of A. Notation ${\displaystyle ^{\top }\!\!A}$ is also used. The symbol ${\displaystyle \top }$ is often replaced by the letter Tort.

2.  For inline uses of the symbol, see ⊤.

□^⊥

1.  Orthogonal complement: If W is a linear subspace of an inner product space V, then ${\displaystyle W^{\bot }}$ denotes its orthogonal complement, that is, the linear space of the elements of V whose inner products with the elements of W are all zero.

2.  Orthogonal subspace in the dual space: If W is a linear subspace (or a submodule) of a vector space (or of a module) V, then ${\displaystyle W^{\bot }}$ may denote the orthogonal subspaceofW, that is, the set of all linear forms that map W to zero.

3.  For inline uses of the symbol, see ⊥.