Normal subgroups of nonstandard symmetric and alternating groups

Richard Kaye, John Allsup

Research output: Contribution to journalArticle

4 Citations (Scopus)


Let M be a nonstandard model of Peano Arithmetic with domain M and let n is an element of M be nonstandard. We study the symmetric and alternating groups S-n and A(n) of permutations of the set {0, 1,..., n-1} internal to M, and classify all their normal subgroups, identifying many externally defined such normal subgroups in the process. We provide evidence that An and Sn are not split extensions by these normal subgroups, by showing that any such complement if it exists, cannot be a limit of definable sets. We conclude by identifying an R-valued metric on S-n=S-n/B-S and A(n)=A(n)/B-A (where B-S, B-A are the maximal normal subgroups of Sn and An identified earlier) making these groups into topological groups, and by showing that if M is N-1-saturated then S-n and A(n) are complete with respect to this metric.
Original languageEnglish
Pages (from-to)107--121
Number of pages15
JournalArchive for Mathematical Logic
Issue number2
Publication statusPublished - 31 Jan 2007


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