# Difference between revisions of "Group isomorphism"

### From Online Dictionary of Crystallography

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− | A '''group isomorphism''' is a special type of [[group homomorphism]]. It is a | + | A '''group isomorphism''' is a special type of [[group homomorphism]]. It is a mapping between two groups that sets up a one-to-one correspondence between the elements of the groups in a way that respects the respective group operations. If there exists an isomorphism between two groups, then the groups are called '''isomorphic'''. Isomorphic groups have the same properties and the same structure of their multiplication table. |

− | Let (''G'', *) and (''H'', #) be two groups, where "*" and "#" are the | + | Let (''G'', *) and (''H'', #) be two groups, where "*" and "#" are the [[binary operation]]s in ''G'' and ''H'', respectively. A ''group isomorphism'' from (''G'', *) to (''H'', #) is a [[Mapping|bijection]] from ''G'' to ''H'', ''i''.''e''. a bijective mapping ''f'' : ''G'' → ''H'' such that for all ''u'' and ''v'' in ''G'' one has |

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− | + | Two groups (''G'', *) and (''H'', #) are isomorphic if an isomorphism between them exists. This is written: | |

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− | If ''H'' = ''G'' and # | + | If ''H'' = ''G'' and the binary operations # and * coincide, the bijection is an [[automorphism]]. |

[[Category:Fundamental crystallography]] | [[Category:Fundamental crystallography]] |

## Revision as of 14:56, 1 April 2009

Isomorphisme entre groupes (*Fr*). Gruppenisomorphismus (*Ge*). Isomorfismo fra gruppi (*It*). 同形 (*Ja*).

A **group isomorphism** is a special type of group homomorphism. It is a mapping between two groups that sets up a one-to-one correspondence between the elements of the groups in a way that respects the respective group operations. If there exists an isomorphism between two groups, then the groups are called **isomorphic**. Isomorphic groups have the same properties and the same structure of their multiplication table.

Let (*G*, *) and (*H*, #) be two groups, where "*" and "#" are the binary operations in *G* and *H*, respectively. A *group isomorphism* from (*G*, *) to (*H*, #) is a bijection from *G* to *H*, *i*.*e*. a bijective mapping *f* : *G* → *H* such that for all *u* and *v* in *G* one has

*f* (*u* * *v*) = *f* (*u*) # *f* (*v*).

Two groups (*G*, *) and (*H*, #) are isomorphic if an isomorphism between them exists. This is written:

(*G*, *) [math]\cong[/math] (*H*, #)

If *H* = *G* and the binary operations # and * coincide, the bijection is an automorphism.