Center is characteristic
This article gives the statement, and possibly proof, of the fact that for any group, the subgroup obtained by applying a given subgroup-defining function (i.e., center) always satisfies a particular subgroup property (i.e., characteristic subgroup)}
View subgroup property satisfactions for subgroup-defining functions View subgroup property dissatisfactions for subgroup-defining functions
Statement
The center of a group is a characteristic subgroup of it.
Related facts
Stronger facts: stronger subgroup properties satisfied
The center satisfies a number of stronger properties:
| Property | Meaning | Proof of satisfaction by center | Proof that it's stronger than characteristicity |
|---|---|---|---|
| strictly characteristic subgroup | invariant under all surjective endomorphisms | Center is strictly characteristic | strictly characteristic implies characteristic |
| quasiautomorphism-invariant subgroup | invariant under all quasiautomorphisms | Center is quasiautomorphism-invariant | quasiautomorphism-invariant implies characteristic |
| purely definable subgroup | can be defined in first-order language using the pure theory of the group | Center is purely definable | purely definable implies characteristic |
| elementarily characteristic subgroup | no other elementarily equivalently embedded subgroups | Center is elementarily characteristic | elementarily characteristic implies characteristic |
| bound-word subgroup | described as set of solutions of a system of equations, other variables quantified | Center is bound-word | (via strictly characteristic) |
Stronger subgroup properties not satisfied
| Property | Meaning | Proof of dissatisfaction | Proof that it is stronger than characteristicity |
|---|---|---|---|
| fully invariant subgroup | invariant under all endomorphisms | center not is fully invariant | fully invariant implies characteristic |
| normal-homomorph-containing subgroup | contains any homomorphic image that is normal in whole group | center not is normal-homomorph-containing | (via strictly characteristic) |
| weakly normal-homomorph-containing subgroup | contains any homomorphic image in a map that sends normal subgroups to normal subgroups | center not is weakly normal-homomorph-containing | (via strictly characteristic) |
| 1-automorphism-invariant subgroup | invariant under all 1-automorphisms | center not is 1-automorphism-invariant | 1-automorphism-invariant implies characteristic |
Weaker facts: weaker subgroup properties satisfied
Analogues in other algebraic structures
- Center is characteristic for Lie rings
- Center is derivation-invariant (another analogue for Lie rings)