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Difference between revisions of "Complete group"

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A group <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c023/c023760/c0237601.png" /> whose centre (cf. [[Centre of a group|Centre of a group]]) is trivial (that is, <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c023/c023760/c0237602.png" /> is a so-called group without centre) and for which all automorphisms are inner (see [[Inner automorphism|Inner automorphism]]). The automorphism group of a complete group <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c023/c023760/c0237603.png" /> is isomorphic to <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c023/c023760/c0237604.png" /> itself (the term  "complete"  is related to this property). Examples of complete groups are the symmetric groups <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c023/c023760/c0237605.png" /> when <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c023/c023760/c0237606.png" /> (cf. [[Symmetric group|Symmetric group]]). If a group <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c023/c023760/c0237607.png" /> contains a normal subgroup which is complete, then <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c023/c023760/c0237608.png" /> decomposes into a direct product <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c023/c023760/c0237609.png" /> of a subgroup <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c023/c023760/c02376010.png" /> and its centralizer in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c023/c023760/c02376011.png" />.
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A group $G$ whose [[Centre of a group|centre]] is trivial (that is, $G$ is a so-called group without centre) and for which all automorphisms are inner (see [[Inner automorphism]]). The automorphism group of a complete group $G$ is isomorphic to $G$ itself (the term  "complete"  is related to this property). Examples of complete groups are the [[symmetric group]]s $S_n$ when $N \ne 2,6$. If a group $G$ contains a normal subgroup $B$ which is complete, then $G$ decomposes into a direct product $B \times K$ of the subgroup $B$ and its centralizer $K$ in $G$; indeed $K$ is isomorphic to the quotient group $G/B$.
  
 
====References====
 
====References====
<table><TR><TD valign="top">[1]</TD> <TD valign="top">  M.I. Kargapolov,  Yu.I. Merzlyakov,  "Fundamentals of group theory" , Moscow  (1982)  (In Russian)</TD></TR><TR><TD valign="top">[2]</TD> <TD valign="top">  M. Hall jr.,  "Group theory" , Chelsea  (1976)</TD></TR></table>
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<table>
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<TR><TD valign="top">[1]</TD> <TD valign="top">  M.I. Kargapolov,  Yu.I. Merzlyakov,  "Fundamentals of group theory" , Moscow  (1982)  (In Russian)</TD></TR>
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<TR><TD valign="top">[2]</TD> <TD valign="top">  M. Hall jr.,  "Group theory" , Chelsea  (1976)</TD></TR>
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</table>
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<table>
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<TR><TD valign="top">[a1]</TD> <TD valign="top">  William Burnside,  "Theory of Groups of Finite Order", 1911 ed. repr. Cambridge University Press (2012) ISBN 1108050328</TD></TR>
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</table>

Revision as of 18:24, 5 December 2014

A group $G$ whose centre is trivial (that is, $G$ is a so-called group without centre) and for which all automorphisms are inner (see Inner automorphism). The automorphism group of a complete group $G$ is isomorphic to $G$ itself (the term "complete" is related to this property). Examples of complete groups are the symmetric groups $S_n$ when $N \ne 2,6$. If a group $G$ contains a normal subgroup $B$ which is complete, then $G$ decomposes into a direct product $B \times K$ of the subgroup $B$ and its centralizer $K$ in $G$; indeed $K$ is isomorphic to the quotient group $G/B$.

References

[1] M.I. Kargapolov, Yu.I. Merzlyakov, "Fundamentals of group theory" , Moscow (1982) (In Russian)
[2] M. Hall jr., "Group theory" , Chelsea (1976)
[a1] William Burnside, "Theory of Groups of Finite Order", 1911 ed. repr. Cambridge University Press (2012) ISBN 1108050328
How to Cite This Entry:
Complete group. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Complete_group&oldid=15667
This article was adapted from an original article by N.N. Vil'yams (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article