Powered group for a set of primes
Contents
Definition
Let be a set of primes. A group
is termed
-powered or uniquely
-divisible if it satisfies the following equivalent definitions:
No. | Shorthand | Explanation |
---|---|---|
1 | ![]() ![]() ![]() |
For every ![]() ![]() ![]() ![]() ![]() ![]() |
2 | unique rational powers with denominators ![]() |
Given any integers ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
3 | group powered over the ring ![]() |
![]() ![]() ![]() ![]() |
4 | ![]() ![]() ![]() ![]() |
There exists a natural number ![]() ![]() ![]() ![]() ![]() |
A rationally powered group is a group powered for the set of all primes.
Localization definition
Let be a set of primes. We call a group
a
-local group if
is powered over all primes not in
. Note that
may also happen to be powered over one or more of the primes in
.
Note in particular that a -local group is a group that is powered over all primes other than
. Note that this definition differs completely from the definition of p-local subgroup.
Powering versus localization terminology
The domains of abstract group theory as well as combinatorial and geometric group theory often use the "powering" or "unique divisibility" jargon. The domain of algebraic topology typically uses the "localization" jargon because of the connection with local nilpotent spaces.
Conjunction with group properties
Conjunction | Other component of conjunction | Facts about the conjunction |
---|---|---|
nilpotent group that is powered over a set of primes | nilpotent group |
Related notions
We can think of forgetful functors:
category of -powered groups
category of groups
category of sets
Note that each of these categories arises from a variety of algebras, and the forgetful functors are variety reduct maps.
Both the two individual functors and their composite have left-adjoint functors. The three left-adjoint functors we obtain are:
Functor source | Functor target | Left adjoint to ... | Description of functor |
---|---|---|---|
category of groups | category of ![]() |
forgetful functor from ![]() |
Every group admits an initial homomorphism to a pi-powered group. The functor sending a group to the image of this initial homomorphism is termed the ![]() ![]() |
category of sets | category of ![]() |
forgetful functor from ![]() |
See free powered group for a set of primes. A detailed existence proof is at there exist free powered groups for any set of primes and any size of generating set. |
category of sets | category of groups | forgetful functor from groups to sets | (abstract) free group functor |
References
Journal references
- Some aspects of groups with unique roots by Gilbert Baumslag, Acta mathematica, Volume 104, Page 217 - 303(Year 1960): PDF (ungated)More info: Baumslag's paper uses the notation
-group for a group powered over the prime set
.
Textbook references
- p-automorphisms of finite p-groups by Evgenii I. Khukhro, 13-digit ISBN 978-0-521-59717-3, 10-digit ISBN 0-521-59717-X, Page 18, Section 1.3 (Algebraic systems, varieties, and free objects), More info