Difference between revisions of "Group"
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A '''group''' <math>G</math> is a [[set]] of elements together with an [[operation]] <math>\cdot:G\times G\to G</math> (the dot is frequently supressed) satisfying the following conditions: | A '''group''' <math>G</math> is a [[set]] of elements together with an [[operation]] <math>\cdot:G\times G\to G</math> (the dot is frequently supressed) satisfying the following conditions: | ||
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Groups frequently arise as [[permutation]]s of collections of objects. For example, the rigid motions of <math>\mathbb{R}^2</math> that fix a certain regular <math>n</math>-gon is a group, called the [[dihedral group]] and denoted in some texts <math>D_{2n}</math> (since it has <math>2n</math> elements) and in others <math>D_n</math> (since it preserves a regular <math>n</math>-gon). Another example of a group is the [[symmetric group]] <math>S_n</math> of all permutations of <math>\{1,2,\ldots,n\}</math>. | Groups frequently arise as [[permutation]]s of collections of objects. For example, the rigid motions of <math>\mathbb{R}^2</math> that fix a certain regular <math>n</math>-gon is a group, called the [[dihedral group]] and denoted in some texts <math>D_{2n}</math> (since it has <math>2n</math> elements) and in others <math>D_n</math> (since it preserves a regular <math>n</math>-gon). Another example of a group is the [[symmetric group]] <math>S_n</math> of all permutations of <math>\{1,2,\ldots,n\}</math>. | ||
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| + | ==See Also== | ||
| + | *[[Field]] | ||
| + | *[[Ring]] | ||
| + | *[[Group theory]] | ||
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| + | {{stub}} | ||
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| + | {{wikify}} | ||
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| + | [[Category:Definition]] | ||
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| + | [[Category:Group theory]] | ||
Revision as of 17:22, 17 November 2007
A group 
is a set of elements together with an operation 
(the dot is frequently supressed) satisfying the following conditions:
- For all
, 
(associativity). - There exists an element
so that for all 
, 
(identity). - For any , there exists
so that 
( inverses).
, 
(
so that for all 
, 
(
so that 
(
One can also thing of groups as monoids with inverses.
Note that the group operation need not be commutative. If the group operation is commutative, we call the group an abelian group (after the Norwegian mathematician Niels Henrik Abel).
Groups frequently arise as permutations of collections of objects. For example, the rigid motions of 
that fix a certain regular 
-gon is a group, called the dihedral group and denoted in some texts 
(since it has 
elements) and in others 
(since it preserves a regular -gon). Another example of a group is the symmetric group 
of all permutations of 
.
See Also
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