# Central factor is transitive

This article gives the statement, and possibly proof, of a subgroup property (i.e., central factor) satisfying a subgroup metaproperty (i.e., transitive subgroup property)

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## Contents

## Statement

Suppose are groups such that is a central factor of and is a central factor of . Then, is a central factor of .

## Definitions used

### Central factor

`Further information: Central factor`

A subgroup of a group is termed a **central factor** of if every inner automorphism of restricts to an inner automorphism of .

In terms of the function restriction expression, this is expressed as:

Inner automorphism Inner automorphism

In other words, every inner automorphism of the whole group restricts to an inner automorphism of the subgroup.

## Related facts

- Central factor implies transitively normal
- Central factor implies conjugacy-closed normal
- Conjugacy-closed normality is transitive

## Proof

### Proof in terms of the function restriction expression

`Further information: Balanced implies transitive`

The property of being a central factor is a balanced subgroup property in terms of the function restriction formalism: it has a function restriction expression where both sides are equal (in this case, equal to the property of being an inner automorphism). Any balanced subgroup property is transitive, and thus, the property of being a central factor is transitive.

### Hands-on proof

**Given**: Groups such that is a central factor of and is a central factor of .

**To prove**: is a central factor of .

**Proof**: We need to show that any inner automorphism of restricts to an inner automorphism of . Suppose is an inner automorphism of .

Since is a central factor of , restricts to an inner automorphism, say , of . Further, since is a central factor of , restricts to an inner automorphism of , say .

Clearly, is also the restriction of to , so restricts to an inner automorphism of .