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{{Algebraic structures}} | |||
In [[mathematics]], and more specifically in [[abstract algebra]], the term '''algebraic structure''' generally refers to an arbitrary [[Set (mathematics)|set]] (called '''carrier set''' or '''underlying set''') with one or more [[finitary operation]]s defined on it.<ref>P.M. Cohn. (1981) ''Universal Algebra'', Springer, p. 41.</ref> | |||
Common examples of algebraic structures include [[group (mathematics)|groups]], [[ring (mathematics)|rings]], [[field (mathematics)|fields]], and [[lattice (order)|lattices]]. More complex algebraic structures can be defined by introducing multiple operations, different underlying sets, or by altering the defining axioms. Examples of more complex structures include [[vector space]]s, [[module (mathematics)|modules]], and [[algebra (ring theory)|algebras]]. | |||
The properties of specific algebraic structures are studied in the branch known as [[abstract algebra]]. The general theory of algebraic [[structure (mathematical logic)|structure]]s has been formalized in [[universal algebra]]. [[Category theory]] is used to study the relationships between two or more classes of algebraic structures, often of different kinds. For example, [[Galois theory]] studies the connection between certain ''fields'' and ''groups'', algebraic structures of two different kinds. | |||
In a slight abuse of notation, the word "structure" can also refer only to the operations on a structure, and not the underlying set itself. For example, a phrase "we have defined a ring ''structure'' (a ''structure'' of ring) on the set <math>A</math>" means that we have defined [[ring (mathematics)|ring]] operations on the set <math>A</math>. For another example, the group <math>(\mathbb Z, +)</math> can be seen as a set <math>\mathbb Z</math> that is equipped with an ''algebraic structure,'' namely the operation <math>+</math>. | |||
==Introduction== | |||
Addition and multiplication on numbers are the prototypical example of an operation that combines two elements of a set to produce a third. These operations obey several algebraic laws. For example ''a'' + (''b'' + ''c'') = (''a'' + ''b'') + ''c'' and ''a''(''bc'') = (''ab'')''c'', both example of the ''associative law''. Also ''a'' + ''b'' = ''b'' + ''a'', and ''ab'' = ''ba'', the ''commutative law.'' Many systems studied by mathematicians have operations that obey some, but not necessarily all, of the laws of ordinary arithmetic. For example, rotations of objects in three-dimensional space can be combined by performing the first rotation and then applying the second rotation to the object in its new orientation. This operation on rotations obeys the associative law, but can fail the commutative law. | |||
Mathematicians give names to sets with one or more operations that obey a particular collection of laws, and study them in the abstract as algebraic structures. When a new problem can be shown to follow the laws of one of these algebraic structures, all the work that has been done on that category in the past can be applied to the new problem. | |||
In full generality, algebraic structures may involve an arbitrary number of sets and operations that can combine more than two elements (higher [[arity]]), but this article focuses on binary operations on one or two sets. The examples here are by no means a complete list, but they are meant to be a representative list and include the most common structures. Longer lists of algebraic structures may be found in the external links and within ''[[:Category:Algebraic structures]].'' Structures are listed in approximate order of increasing complexity. | |||
==Examples== | |||
===One set with operations=== | |||
'''Simple structures''': '''No''' [[binary operation]]: | |||
* [[Set (mathematics)|Set]]: a degenerate algebraic structure having no operations. | |||
* [[Pointed set]]: ''S'' has one or more distinguished elements, often 0, 1, or both. | |||
* Unary system: ''S'' and a single [[unary operation]] over ''S''. | |||
* Pointed unary system: a unary system with ''S'' a pointed set. | |||
'''Group-like structures''': '''One''' binary operation. The binary operation can be indicated by any symbol, or with no symbol (juxtaposition) as is done for ordinary multiplication of real numbers. | |||
* [[Magma (algebra)|Magma or groupoid]]: ''S'' and a single binary operation over ''S''. | |||
* [[Semigroup]]: an [[associative]] magma. | |||
* [[Monoid]]: a semigroup with [[Identity element|identity]]. | |||
* [[Group (mathematics)|Group]]: a monoid with a unary operation (inverse), giving rise to [[inverse element]]s. | |||
* [[Abelian group]]: a group whose binary operation is [[commutative]]. | |||
* [[Semilattice]]: a semigroup whose operation is [[idempotence|idempotent]] and commutative. The binary operation can be called either [[meet (mathematics)|meet]] or [[join (mathematics)|join]]. | |||
'''Ring-like structures''' or '''Ringoids''': '''Two''' binary operations, often called [[addition]] and [[multiplication]], with multiplication [[distributivity|distributing]] over addition. | |||
* [[Semiring]]: a ringoid such that ''S'' is a monoid under each operation. Addition is typically assumed to be commutative and associative, and the monoid product is assumed to distribute over the addition on both sides, and the additive identity satisfies 0 ''x'' = 0 for all ''x''. | |||
* [[Near-ring]]: a semiring whose additive monoid is a (not necessarily Abelian) group. | |||
* [[Ring (mathematics)|Ring]]: a semiring whose additive monoid is an Abelian group. | |||
* [[Lie ring]]: a ringoid whose additive monoid is an abelian group, but whose multiplicative operation satisfies the [[Jacobi identity]] rather than associativity. | |||
* [[Boolean ring]]: a commutative ring with idempotent multiplication operation. | |||
* [[field (mathematics)|Field]]: a commutative ring which contains a multiplicative inverse for every nonzero element | |||
* [[Kleene algebra]]s: a semiring with idempotent addition and a unary operation, the [[Kleene star]], satisfying additional properties. | |||
* [[*-algebra]]: a ring with an additional unary operation (*) satisfying additional properties. | |||
'''Lattice structures''': '''Two''' or more binary operations, including operations called [[meet and join]], connected by the [[absorption law]].<ref>Ringoids and [[Lattice (order)|lattice]]s can be clearly distinguished despite both having two defining binary operations. In the case of ringoids, the two operations are linked by the [[distributive law]]; in the case of lattices, they are linked by the [[absorption law]]. Ringoids also tend to have numerical [[model theory|model]]s, while lattices tend to have [[set theory|set-theoretic]] models. | |||
</ref> | |||
* [[Complete lattice]]: a lattice in which arbitrary [[meet and join]]s exist. | |||
* [[Bounded lattice]]: a lattice with a [[greatest element]] and least element. | |||
* [[Complemented lattice]]: a bounded lattice with a unary operation, complementation, denoted by [[reverse Polish notation|postfix]] <sup>[[⊥]]</sup><!-- or [[prefix notation|prefix]] [[¬]]-->. The join of an element with its complement is the greatest element, and the meet of the two elements is the least element. | |||
* [[Modular lattice]]: a lattice whose elements satisfy the additional ''modular identity''. | |||
* [[Distributive lattice]]: a lattice in which each of meet and join [[distributive lattice|distributes]] over the other. Distributive lattices are modular, but the converse does not hold. | |||
* [[Boolean algebra (structure)|Boolean algebra]]: a complemented distributive lattice. Either of meet or join can be defined in terms of the other and complementation. This can be shown to be equivalent with the ring-like structure of the same name above. | |||
* [[Heyting algebra]]: a bounded distributive lattice with an added binary operation, [[relative pseudo-complement]], denoted by [[infix]] →, and governed by the axioms ''x'' → ''x'' = 1, ''x'' (''x'' → ''y'') = ''x y'', ''y'' (''x'' → ''y'') = ''y'', ''x'' → (''y z'') = (''x'' → ''y'') (''x'' → ''z''). | |||
'''Arithmetics''': '''Two''' [[binary operation]]s, addition and multiplication. ''S'' is an [[infinite set]]. Arithmetics are pointed unary systems, whose [[unary operation]] is [[injective]] [[successor function|successor]], and with distinguished element 0. | |||
*[[Robinson arithmetic]]. Addition and multiplication are [[Recursion|recursively]] defined by means of successor. 0 is the identity element for addition, and annihilates multiplication. Robinson arithmetic is listed here even though it is a variety, because of its closeness to Peano arithmetic. | |||
* [[Peano arithmetic]]. Robinson arithmetic with an [[axiom schema]] of [[mathematical induction|induction]]. Most ring and field axioms bearing on the properties of addition and multiplication are theorems of Peano arithmetic or of proper extensions thereof. | |||
===Two sets with operations=== | |||
'''[[module (mathematics)|Module]]-like structures:''' composite systems involving two sets and employing at least two binary operations. | |||
* [[Group with operators]]: a group ''G'' with a set Ω and a binary operation Ω × ''G'' → ''G'' satisfying certain axioms. | |||
*[[module (mathematics)|Module]]: an Abelian group ''M'' and a ring ''R'' acting as operators on ''M''. The members of ''R'' are sometimes called [[scalar (mathematics)|scalar]]s, and the binary operation of ''scalar multiplication'' is a function ''R'' × ''M'' → ''M'', which satisfies several axioms. Counting the ring operations these systems have at least three operations. | |||
*[[Vector space]]: a module where the ring ''R'' is a [[division ring]] or [[field (mathematics)|field]]. | |||
*[[Graded vector space]]: a vector space with a [[Direct sum of modules|direct sum]] decomposition breaking the space into "grades". | |||
*[[Quadratic space]]: a vector space ''V'' over a field ''F'' with a function from ''V'' into ''F'' satisfying certain properties. Every quadratic space is also an inner product space (see below). | |||
'''[[algebra (ring theory)|Algebra]]-like structures''': composite system defined over two sets, a ring ''R'' and a ''R'' module ''M'' equipped with an operation called multiplication. This can be viewed as a system with five binary operations: two operations on ''R'', two on ''M'' and one involving both ''R'' and ''M''. | |||
*[[Algebra over a ring]] (also ''R-algebra''): a module over a [[commutative ring]] ''R'', which also carries a multiplication operation that is compatible with the module structure. This includes distributivity over addition and [[Bilinear map|linearity]] with respect to multiplication by elements of ''R''. The theory of an [[algebra over a field]] is especially well developed. | |||
*[[Associative algebra]]: an algebra over a ring such that the multiplication is [[associative property|associative]]. | |||
*[[Nonassociative algebra]]: a module over a commutative ring, equipped with a ring multiplication operation that is not necessarily associative. Often associativity is replaced with a different identity, such as [[alternative algebra|alternation]], the [[Jacobi identity]], or the [[Jordan identity]]. | |||
*[[Coalgebra]]: a vector space with a "comultiplication" defined dually to that of associative algebras. | |||
*[[Lie algebra]]: a special type of nonassociative algebra whose product satisfies the [[Jacobi identity]]. | |||
*[[Lie coalgebra]]: a vector space with a "comultiplication" defined dually to that of Lie algebras. | |||
*[[Graded algebra]]: a graded vector space with an algebra structure compatible with the grading. The idea is that if the grades of two elements ''a'' and ''b'' are known, then the grade of ''ab'' is known, and so the location of the product ''ab'' is determined in the decomposition. | |||
*[[Inner product space]]: an ''F'' vector space ''V'' with a bilinear binary operation from ''V'' × ''V'' → ''F''. | |||
'''Three''' [[binary operation]]s: | |||
*[[Quasigroup]]: may be represented as an algebraic structure with one or three binary operations.<ref>{{cite book | |||
| title =An Introduction to Quasigroups and Their Representations | |||
| author =Jonathan D. H. Smith | |||
| publisher =Chapman & Hall | |||
| url =http://books.google.co.uk/books?id=NfWlUZSOwSkC&printsec=frontcover&dq=quasigroups&source=bl&ots=8ZOf4xvSh6&sig=MyWk4X7vHJL3WkJtPq-Rq3NhLns&hl=en&sa=X&ei=F9caUMjEG4eb1AWAhYGQAw&redir_esc=y#v=onepage&q=quasigroups&f=false | |||
| accessdate = 2012-08-02 }}</ref> | |||
'''Four''' or more binary operations: | |||
*[[Bialgebra]]: an associative algebra with a compatible coalgebra structure. | |||
*[[Lie bialgebra]]: a Lie algebra with a compatible bialgebra structure. | |||
*[[Clifford algebra]]: a graded associative algebra equipped with an [[exterior product]] from which may be derived several possible inner products. [[Exterior algebra]]s and [[geometric algebra]]s are special cases of this construction. | |||
==Hybrid structures== | |||
Algebraic structures can also coexist with added structure of a non-algebraic nature, such as a partial order or a [[topology]]. The added structure must be compatible, in some sense, with the algebraic structure. | |||
* [[Topological group]]: a group with a topology compatible with the group operation. | |||
* [[Lie group]]: a topological group with a compatible smooth [[manifold]] structure. | |||
* [[Ordered group]]s, [[ordered ring]]s and [[ordered field]]s: each type of structure with a compatible [[partial order]]. | |||
* [[Archimedean group]]: a linearly ordered group for which the [[Archimedean property]] holds. | |||
* [[Topological vector space]]: a vector space whose ''M'' has a compatible topology. | |||
* [[Normed vector space]]: a vector space with a compatible [[norm (mathematics)|norm]]. If such a space is [[complete metric space|complete]] (as a metric space) then it is called a [[Banach space]]. | |||
* [[Hilbert space]]: an inner product space over the real or complex numbers whose inner product gives rise to a Banach space structure. | |||
* [[Vertex operator algebra]] | |||
* [[Von Neumann algebra]]: a *-algebra of operators on a Hilbert space equipped with the [[weak operator topology]]. | |||
==Universal algebra== | |||
Algebraic structures are defined through different configurations of [[axiom]]s. [[Universal algebra]] abstractly studies such objects. One major dichotomy is between structures that are axiomatized entirely by ''identities'' and structures that are not. If all axioms defining a class of algebras are identities, then the class of objects is a [[variety (universal algebra)|variety]] (not to be confused with [[algebraic variety]] in the sense of [[algebraic geometry]]). | |||
Identities are equations formulated using only the operations the structure allows, and variables that are tacitly [[universal quantifier|universally quantified]] over the relevant [[universe (mathematics)|universe]]. Identities contain no [[Logical connective|connectives]], [[quantification|existentially quantified variables]], or [[finitary relation|relations]] of any kind other than the allowed operations. The study of varieties is an important part of [[universal algebra]]. An algebraic structure in a variety may be understood as the [[quotient algebra]] of term algebra (also called "absolutely [[free object|free algebra]]") divided by the equivalence relations generated by a set of identities. So, a collection of functions with given [[signature (logic)|signatures]] generate a free algebra, the [[term algebra]] ''T''. Given a set of equational identities (the axioms), one may consider their symmetric, transitive closure ''E''. The [[quotient algebra]] ''T''/''E'' is then the algebraic structure or variety. Thus, for example, groups have a signature containing two operators: the multiplication operator ''m'', taking two arguments, and the inverse operator ''i'', taking one argument, and the identity element ''e'', a constant, which may be considered an operator that takes zero arguments. Given a (countable) set of variables ''x'', ''y'', ''z'', etc. the term algebra is the collection of all possible [[term (mathematics)|terms]] involving ''m'', ''i'', ''e'' and the variables; so for example, ''m(i(x), m(x,m(y,e)))'' would be an element of the term algebra. One of the axioms defining a group is the identity ''m(x, i(x)) = e''; another is ''m(x,e) = x''. The axioms can be represented as [http://ncatlab.org/nlab/show/variety+of+algebras#examples_4 trees]. These equations induce [[equivalence class]]es on the free algebra; the quotient algebra then has the algebraic structure of a group. | |||
Several non-variety structures fail to be varieties, because either: | |||
#It is necessary that 0 ≠ 1, 0 being the additive [[identity element]] and 1 being a multiplicative identity element, but this is a nonidentity; | |||
#Structures such as fields have some axioms that hold only for nonzero members of ''S''. For an algebraic structure to be a variety, its operations must be defined for ''all'' members of ''S''; there can be no partial operations. | |||
Structures whose axioms unavoidably include nonidentities are among the most important ones in mathematics, e.g., [[Field (mathematics)|field]]s and hence also [[vector space]]s and [[algebra (ring theory)|algebra]]s. Although structures with nonidentities retain an undoubted algebraic flavor, they suffer from defects varieties do not have. For example, the product of two [[field (mathematics)|field]]s is not a field. | |||
==Category theory== | |||
[[Category theory]] is another tool for studying algebraic structures (see, for example, Mac Lane 1998). A category is a collection of ''objects'' with associated ''morphisms.'' Every algebraic structure has its own notion of [[homomorphism]], namely any [[function (mathematics)|function]] compatible with the operation(s) defining the structure. In this way, every algebraic structure gives rise to a [[category theory|category]]. For example, the [[category of groups]] has all [[Group (mathematics)|groups]] as objects and all [[group homomorphism]]s as morphisms. This [[concrete category]] may be seen as a [[category of sets]] with added category-theoretic [[structure (category theory)|structure]]. Likewise, the category of [[topological group]]s (whose morphisms are the continuous group homomorphisms) is a [[category of topological spaces]] with extra structure. A [[forgetful functor]] between categories of algebraic structures "forgets" a part of a structure. | |||
There are various concepts in category theory that try to capture the algebraic character of a context, for instance | |||
*[[algebraic category]] | |||
*[[essentially algebraic category]] | |||
*[[presentable category]] | |||
*[[locally presentable category]] | |||
*[[Monad (category theory)|monadic]] functors and categories | |||
*[[universal property]]. | |||
==See also== | |||
* [[Free object]] | |||
* [[List of algebraic structures]] | |||
* [[List of first order theories]] | |||
* [[Signature (logic)|signature]] | |||
* [[Structure (mathematical logic)]] | |||
==References== | |||
{{reflist}} | |||
* {{Citation | last1=Mac Lane | first1=Saunders | author1-link=Saunders Mac Lane | last2=Birkhoff | first2=Garrett | author2-link=Garrett Birkhoff | title=Algebra | publisher=AMS Chelsea | edition=2nd | isbn=978-0-8218-1646-2 | year=1999}} | |||
* {{Citation | last1=Michel | first1=Anthony N. | last2=Herget | first2=Charles J. | title=Applied Algebra and Functional Analysis | publisher=[[Dover Publications]] | location=New York | isbn=978-0-486-67598-5 | year=1993}} | |||
A monograph available online: | |||
* {{Citation | last1=Burris | first1=Stanley N. | last2=Sankappanavar | first2=H. P. | title=A Course in Universal Algebra | url=http://www.thoralf.uwaterloo.ca/htdocs/ualg.html | publisher=[[Springer-Verlag]] | location=Berlin, New York | isbn=978-3-540-90578-3 | year=1981}} | |||
Category theory: | |||
* {{Citation | last1=Mac Lane | first1=Saunders | author1-link=Saunders Mac Lane | title=[[Categories for the Working Mathematician]] | publisher=Springer-Verlag | location=Berlin, New York | edition=2nd | isbn=978-0-387-98403-2 | year=1998}} | |||
* {{Citation | last1=Taylor | first1=Paul | title=Practical foundations of mathematics | publisher=[[Cambridge University Press]] | isbn=978-0-521-63107-5 | year=1999}} | |||
==External links== | |||
* [http://math.chapman.edu/~jipsen/structures/doku.php Jipsen's algebra structures.] Includes many structures not mentioned here. | |||
*[http://mathworld.wolfram.com/topics/Algebra.html Mathworld] page on abstract algebra. | |||
*[[Stanford Encyclopedia of Philosophy]]: [http://plato.stanford.edu/entries/algebra/ Algebra] by [[Vaughan Pratt]]. | |||
[[Category:Abstract algebra]] | |||
[[Category:Algebraic structures]] | |||
[[Category:Mathematical structures]] |
Revision as of 21:46, 6 August 2013
In mathematics, and more specifically in abstract algebra, the term algebraic structure generally refers to an arbitrary set (called carrier set or underlying set) with one or more finitary operations defined on it.[1]
Common examples of algebraic structures include groups, rings, fields, and lattices. More complex algebraic structures can be defined by introducing multiple operations, different underlying sets, or by altering the defining axioms. Examples of more complex structures include vector spaces, modules, and algebras.
The properties of specific algebraic structures are studied in the branch known as abstract algebra. The general theory of algebraic structures has been formalized in universal algebra. Category theory is used to study the relationships between two or more classes of algebraic structures, often of different kinds. For example, Galois theory studies the connection between certain fields and groups, algebraic structures of two different kinds.
In a slight abuse of notation, the word "structure" can also refer only to the operations on a structure, and not the underlying set itself. For example, a phrase "we have defined a ring structure (a structure of ring) on the set " means that we have defined ring operations on the set . For another example, the group can be seen as a set that is equipped with an algebraic structure, namely the operation .
Introduction
Addition and multiplication on numbers are the prototypical example of an operation that combines two elements of a set to produce a third. These operations obey several algebraic laws. For example a + (b + c) = (a + b) + c and a(bc) = (ab)c, both example of the associative law. Also a + b = b + a, and ab = ba, the commutative law. Many systems studied by mathematicians have operations that obey some, but not necessarily all, of the laws of ordinary arithmetic. For example, rotations of objects in three-dimensional space can be combined by performing the first rotation and then applying the second rotation to the object in its new orientation. This operation on rotations obeys the associative law, but can fail the commutative law.
Mathematicians give names to sets with one or more operations that obey a particular collection of laws, and study them in the abstract as algebraic structures. When a new problem can be shown to follow the laws of one of these algebraic structures, all the work that has been done on that category in the past can be applied to the new problem.
In full generality, algebraic structures may involve an arbitrary number of sets and operations that can combine more than two elements (higher arity), but this article focuses on binary operations on one or two sets. The examples here are by no means a complete list, but they are meant to be a representative list and include the most common structures. Longer lists of algebraic structures may be found in the external links and within Category:Algebraic structures. Structures are listed in approximate order of increasing complexity.
Examples
One set with operations
Simple structures: No binary operation:
- Set: a degenerate algebraic structure having no operations.
- Pointed set: S has one or more distinguished elements, often 0, 1, or both.
- Unary system: S and a single unary operation over S.
- Pointed unary system: a unary system with S a pointed set.
Group-like structures: One binary operation. The binary operation can be indicated by any symbol, or with no symbol (juxtaposition) as is done for ordinary multiplication of real numbers.
- Magma or groupoid: S and a single binary operation over S.
- Semigroup: an associative magma.
- Monoid: a semigroup with identity.
- Group: a monoid with a unary operation (inverse), giving rise to inverse elements.
- Abelian group: a group whose binary operation is commutative.
- Semilattice: a semigroup whose operation is idempotent and commutative. The binary operation can be called either meet or join.
Ring-like structures or Ringoids: Two binary operations, often called addition and multiplication, with multiplication distributing over addition.
- Semiring: a ringoid such that S is a monoid under each operation. Addition is typically assumed to be commutative and associative, and the monoid product is assumed to distribute over the addition on both sides, and the additive identity satisfies 0 x = 0 for all x.
- Near-ring: a semiring whose additive monoid is a (not necessarily Abelian) group.
- Ring: a semiring whose additive monoid is an Abelian group.
- Lie ring: a ringoid whose additive monoid is an abelian group, but whose multiplicative operation satisfies the Jacobi identity rather than associativity.
- Boolean ring: a commutative ring with idempotent multiplication operation.
- Field: a commutative ring which contains a multiplicative inverse for every nonzero element
- Kleene algebras: a semiring with idempotent addition and a unary operation, the Kleene star, satisfying additional properties.
- *-algebra: a ring with an additional unary operation (*) satisfying additional properties.
Lattice structures: Two or more binary operations, including operations called meet and join, connected by the absorption law.[2]
- Complete lattice: a lattice in which arbitrary meet and joins exist.
- Bounded lattice: a lattice with a greatest element and least element.
- Complemented lattice: a bounded lattice with a unary operation, complementation, denoted by postfix ⊥. The join of an element with its complement is the greatest element, and the meet of the two elements is the least element.
- Modular lattice: a lattice whose elements satisfy the additional modular identity.
- Distributive lattice: a lattice in which each of meet and join distributes over the other. Distributive lattices are modular, but the converse does not hold.
- Boolean algebra: a complemented distributive lattice. Either of meet or join can be defined in terms of the other and complementation. This can be shown to be equivalent with the ring-like structure of the same name above.
- Heyting algebra: a bounded distributive lattice with an added binary operation, relative pseudo-complement, denoted by infix →, and governed by the axioms x → x = 1, x (x → y) = x y, y (x → y) = y, x → (y z) = (x → y) (x → z).
Arithmetics: Two binary operations, addition and multiplication. S is an infinite set. Arithmetics are pointed unary systems, whose unary operation is injective successor, and with distinguished element 0.
- Robinson arithmetic. Addition and multiplication are recursively defined by means of successor. 0 is the identity element for addition, and annihilates multiplication. Robinson arithmetic is listed here even though it is a variety, because of its closeness to Peano arithmetic.
- Peano arithmetic. Robinson arithmetic with an axiom schema of induction. Most ring and field axioms bearing on the properties of addition and multiplication are theorems of Peano arithmetic or of proper extensions thereof.
Two sets with operations
Module-like structures: composite systems involving two sets and employing at least two binary operations.
- Group with operators: a group G with a set Ω and a binary operation Ω × G → G satisfying certain axioms.
- Module: an Abelian group M and a ring R acting as operators on M. The members of R are sometimes called scalars, and the binary operation of scalar multiplication is a function R × M → M, which satisfies several axioms. Counting the ring operations these systems have at least three operations.
- Vector space: a module where the ring R is a division ring or field.
- Graded vector space: a vector space with a direct sum decomposition breaking the space into "grades".
- Quadratic space: a vector space V over a field F with a function from V into F satisfying certain properties. Every quadratic space is also an inner product space (see below).
Algebra-like structures: composite system defined over two sets, a ring R and a R module M equipped with an operation called multiplication. This can be viewed as a system with five binary operations: two operations on R, two on M and one involving both R and M.
- Algebra over a ring (also R-algebra): a module over a commutative ring R, which also carries a multiplication operation that is compatible with the module structure. This includes distributivity over addition and linearity with respect to multiplication by elements of R. The theory of an algebra over a field is especially well developed.
- Associative algebra: an algebra over a ring such that the multiplication is associative.
- Nonassociative algebra: a module over a commutative ring, equipped with a ring multiplication operation that is not necessarily associative. Often associativity is replaced with a different identity, such as alternation, the Jacobi identity, or the Jordan identity.
- Coalgebra: a vector space with a "comultiplication" defined dually to that of associative algebras.
- Lie algebra: a special type of nonassociative algebra whose product satisfies the Jacobi identity.
- Lie coalgebra: a vector space with a "comultiplication" defined dually to that of Lie algebras.
- Graded algebra: a graded vector space with an algebra structure compatible with the grading. The idea is that if the grades of two elements a and b are known, then the grade of ab is known, and so the location of the product ab is determined in the decomposition.
- Inner product space: an F vector space V with a bilinear binary operation from V × V → F.
Three binary operations:
- Quasigroup: may be represented as an algebraic structure with one or three binary operations.[3]
Four or more binary operations:
- Bialgebra: an associative algebra with a compatible coalgebra structure.
- Lie bialgebra: a Lie algebra with a compatible bialgebra structure.
- Clifford algebra: a graded associative algebra equipped with an exterior product from which may be derived several possible inner products. Exterior algebras and geometric algebras are special cases of this construction.
Hybrid structures
Algebraic structures can also coexist with added structure of a non-algebraic nature, such as a partial order or a topology. The added structure must be compatible, in some sense, with the algebraic structure.
- Topological group: a group with a topology compatible with the group operation.
- Lie group: a topological group with a compatible smooth manifold structure.
- Ordered groups, ordered rings and ordered fields: each type of structure with a compatible partial order.
- Archimedean group: a linearly ordered group for which the Archimedean property holds.
- Topological vector space: a vector space whose M has a compatible topology.
- Normed vector space: a vector space with a compatible norm. If such a space is complete (as a metric space) then it is called a Banach space.
- Hilbert space: an inner product space over the real or complex numbers whose inner product gives rise to a Banach space structure.
- Vertex operator algebra
- Von Neumann algebra: a *-algebra of operators on a Hilbert space equipped with the weak operator topology.
Universal algebra
Algebraic structures are defined through different configurations of axioms. Universal algebra abstractly studies such objects. One major dichotomy is between structures that are axiomatized entirely by identities and structures that are not. If all axioms defining a class of algebras are identities, then the class of objects is a variety (not to be confused with algebraic variety in the sense of algebraic geometry).
Identities are equations formulated using only the operations the structure allows, and variables that are tacitly universally quantified over the relevant universe. Identities contain no connectives, existentially quantified variables, or relations of any kind other than the allowed operations. The study of varieties is an important part of universal algebra. An algebraic structure in a variety may be understood as the quotient algebra of term algebra (also called "absolutely free algebra") divided by the equivalence relations generated by a set of identities. So, a collection of functions with given signatures generate a free algebra, the term algebra T. Given a set of equational identities (the axioms), one may consider their symmetric, transitive closure E. The quotient algebra T/E is then the algebraic structure or variety. Thus, for example, groups have a signature containing two operators: the multiplication operator m, taking two arguments, and the inverse operator i, taking one argument, and the identity element e, a constant, which may be considered an operator that takes zero arguments. Given a (countable) set of variables x, y, z, etc. the term algebra is the collection of all possible terms involving m, i, e and the variables; so for example, m(i(x), m(x,m(y,e))) would be an element of the term algebra. One of the axioms defining a group is the identity m(x, i(x)) = e; another is m(x,e) = x. The axioms can be represented as trees. These equations induce equivalence classes on the free algebra; the quotient algebra then has the algebraic structure of a group.
Several non-variety structures fail to be varieties, because either:
- It is necessary that 0 ≠ 1, 0 being the additive identity element and 1 being a multiplicative identity element, but this is a nonidentity;
- Structures such as fields have some axioms that hold only for nonzero members of S. For an algebraic structure to be a variety, its operations must be defined for all members of S; there can be no partial operations.
Structures whose axioms unavoidably include nonidentities are among the most important ones in mathematics, e.g., fields and hence also vector spaces and algebras. Although structures with nonidentities retain an undoubted algebraic flavor, they suffer from defects varieties do not have. For example, the product of two fields is not a field.
Category theory
Category theory is another tool for studying algebraic structures (see, for example, Mac Lane 1998). A category is a collection of objects with associated morphisms. Every algebraic structure has its own notion of homomorphism, namely any function compatible with the operation(s) defining the structure. In this way, every algebraic structure gives rise to a category. For example, the category of groups has all groups as objects and all group homomorphisms as morphisms. This concrete category may be seen as a category of sets with added category-theoretic structure. Likewise, the category of topological groups (whose morphisms are the continuous group homomorphisms) is a category of topological spaces with extra structure. A forgetful functor between categories of algebraic structures "forgets" a part of a structure.
There are various concepts in category theory that try to capture the algebraic character of a context, for instance
- algebraic category
- essentially algebraic category
- presentable category
- locally presentable category
- monadic functors and categories
- universal property.
See also
- Free object
- List of algebraic structures
- List of first order theories
- signature
- Structure (mathematical logic)
References
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- Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010
A monograph available online:
- Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010
Category theory:
- Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010
External links
- Jipsen's algebra structures. Includes many structures not mentioned here.
- Mathworld page on abstract algebra.
- Stanford Encyclopedia of Philosophy: Algebra by Vaughan Pratt.
- ↑ P.M. Cohn. (1981) Universal Algebra, Springer, p. 41.
- ↑ Ringoids and lattices can be clearly distinguished despite both having two defining binary operations. In the case of ringoids, the two operations are linked by the distributive law; in the case of lattices, they are linked by the absorption law. Ringoids also tend to have numerical models, while lattices tend to have set-theoretic models.
- ↑ 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
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