Prüfer rank

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In mathematics, especially in the area of algebra known as group theory, the Prüfer rank of a pro-p group measures the size of a group in terms of the ranks of its elementary abelian sections. The rank is well behaved and helps to define analytic pro-p-groups. The term is named after Heinz Prüfer.

[edit] Definition

The Prüfer rank of pro-p-group G is

\sup\{d(H)|H\leq G\}

where d(H) is the rank of the abelian group

H / Φ(H),

where Φ(H) is the Frattini subgroup of H.

As the Frattini subgroup of H can be thought of as the group of non-generating elements of H, it can be seen that d(H) will be equal to the size of any minimal generating set of H.

[edit] Properties

Those profinite groups with finite Prüfer rank are more amenable to analysis.

Specifically in the case of finitely generated pro-p groups, having finite Prüfer rank is equivalent to having an open normal subgroup that is powerful. In turn these are precisely the class of pro-p groups that are p-adic analytic - that is groups that can be imbued with a p-adic manifold structure.

[edit] References