Sheng Li (gmachine1729) wrote,
Sheng Li

A observation on conjugate subgroups

Originally published at 狗和留美者不得入内. You can comment here or there.

Let H and H' be conjugate subgroups of G, that is, for some g \in G, g^{-1}Hg = H'. Equivalently, HgH' = gH', which means there is some element of G/H' such that under the action of H on G/H', its stabilizer subgroup is H, all of the group of the group action. Suppose H is a p-group with index with respect to G non-divisible by p. Then such a fully stabilized coset must exist by the following lemma.

If H is a p-group that acts on \Omega, then |\Omega| = |\Omega_0|\;(\mathrm{mod\;} p), where \Omega_0 is the subset of \Omega of elements fully stabilized by H.

Its proof rests on the use orbit stabilizer theorem to vanish out orbits that are multiples of p.

This is the natural origin of the second Sylow theorem.

Tags: algebra, group theory, 数学/математика

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