Group Epimorphism preserves Central Subgroups
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Theorem
Let $G$ and $H$ be groups.
Let $\theta: G \to H$ be an epimorphism.
Let $Z \le G$ be a central subgroup of $G$.
Then $\theta \sqbrk Z$ is a central subgroup of $H$.
Proof
By definition of central subgroup:
- $Z \subseteq \map Z G$
where $\map Z G$ denotes the center of $G$.
From Image under Epimorphism of Center is Subset of Center:
- $\theta \sqbrk {\map Z G} \subseteq \map Z H$
From Image of Subset under Mapping is Subset of Image it follows that:
- $\theta \sqbrk Z \subseteq \map Z H$
The result follows.
$\blacksquare$