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Finitely GeneratedSuppose G is finitley generated group for every n prove that there are finite subgroups like H such that [G:H]=n |

Re: Finitely GeneratedQuote:
Now, it is NOT true that if G is a f.g. group then for any n (natural number?) there's a sbgp. of index n. Just take some finite group and let n be a natural number that does NOT divide the order of G... Tonio |

I tried to add the infiniteness but I am unable even to start. If that kind of problem is not open, there must be some pretty heavy results behind ... |

I mean G is a group which is finitely generated and n is natural number .prove that there are finite subgroups like H such that [G:H]=n. |

Quote:
Again, this is NOT true. If G is finite, then there are plenty of counterexamples for plenty of natural numbers....for example, no group of order 36 has a sbgp. of index 7,5, 11 or 23. Now if G is infinite, then if H is finite the index [G:H] HAS to be infinite, so the question AGAIN makes no sense Tonio |

let G=<a1,...,am>. If |G:H|=n, we can get the generators of H by the coset representatives. We know the are finite many different representatives by Reidemester-Schreier system. |

Quote:
Revisiting the site after sometime I think I may, probably, know what the OP meant to ask: he wants to prove that if G is a f.g. group, then for any natural number n there's a finite number of sbgps. H of G s.t. [G:H] = n. If this is what he meant to ask....wow, dude! Please do improve your english! Anyway you'll need it to make a reasonably worthwhile career in maths since a huge ammount of professional papers and books are in english. Anyway: Let H <= G be s.t. [G:H] = n ==> by the regular representation of G in the set of left cosets of H in G, we get a homomorphism G --> S_n. Since any homom. from G to any group is uniquely determined by its action on any set of generators of G, and since G is fin. generated (say, by g1,..., gr), there thus are at most (n!)^r homom. from G into S_n, and since any sbgp. H as above gives rise to one of these, there are at most (n!)^r sbgps. of G of index n. Regards Tonio |

Tonio, I can't see how the representation you mention uniquely determines H. There might be more than one H giving rise to the same permutation representation. This is true already for the subgroups of order 2 in Z/2Z x Z/2Z. /d |

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