Group Algebras: Normal Subgroups and Ideals

被引:0
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作者
Rüdiger Göbel
Otto H. Kegel
机构
[1] Universität Duisburg-Essen,Fachbereich Mathematik
[2] Albert-Ludwigs-Universität Freiburg,Mathematisches Institut
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Primary 20C07, 20B35; Secondary 20E45, 16D25; Ideals of group rings; normal subgroups; factors of full symmetric groups;
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摘要
The standard correspondence between the normal subgroups of the group G and some ideals of the group algebra FG is described. There is the problem of what we can say (or even prove) about a two-sided ideal \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$I \neq (0)$$ \end{document} of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${\mathbb{F}}G$$ \end{document} that does not contain any element of the form 1 − g ≠ 0, g ∈G of the standard basis of the augmentation ideal of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${\mathbb{F}}G$$ \end{document} . The main part of the argument of [2] yields the insight that, for such an ideal I there exists an expansion \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$H \supseteq G$$ \end{document} such that the ideal J of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${\mathbb{F}}H$$ \end{document} spanned by I contains an element 1 − h, h ∈ H \ G. Using the ideas of [2], we construct \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${\mathbb{F}}$$ \end{document} -thick groups H such that for every ideal J ≠ (0) of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${\mathbb{F}}H$$ \end{document} there are elements 1 − h ≠ 0 in J. This construction allows many variations. Examples of simple \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${\mathbb{F}}$$ \end{document} -thick groups were pointed out in [2]. A natural class of (in general non-simple) \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${\mathbb{F}}$$ \end{document} -full groups are the normal sections of the groups \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$S^{\prime} := \rm{Sym}({\it M})/ \rm{Fin}({\it M})\,\rm{for\,any\,infinite\,set} {\it M}.$$ \end{document}(Here, Fin(M) is the subgroup of all finitary permutations of M.)
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页码:323 / 332
页数:9
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