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can someone please tell me? I couldn't find a reference in the paper I was reading.

Yemon Choi
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asked Feb 16 2010 at 3:56

Dave
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Note that this fact is only true in finitely generated groups. – HW Feb 16 2010 at 5:21

Jason Dyer · Answer 1 · 2010-02-16 04:23:59Z UTC

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Subgroups of finite index in free groups. Canadian J.Math., 1:187–190, 1949.

answered Feb 16 2010 at 4:23

Jason Dyer
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This is not a result of Hall; Hall counted precisely the number of such subgroups. Here are links to the paper: cms.math.ca/cjm/v1/p187 ams.org/mathscinet-getitem?mr=28836 – Jack Schmidt Feb 16 2010 at 5:00

david mccune · Answer 2 · 2010-02-16 06:12:39Z UTC

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Thanks for the help.

answered Feb 16 2010 at 6:12

Name of the Marshall Hall paper in which he proved that the intersection of all subgroups of a fixed finite index is again finite index?