Homomorphism to Group Preserves Identity
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Theorem
Let $\struct {S, \circ}$ be an algebraic structure.
Let $\struct {T, *}$ be a group.
Let $\phi: \struct {S, \circ} \to \struct {T, *}$ be a homomorphism.
Let $\struct {S, \circ}$ have an identity $e_S$.
Then:
- $\map \phi {e_S} = e_T$
Proof
By hypothesis, $\struct {T, *}$ is a group.
By the Cancellation Laws, all elements of $T$ are cancellable.
Thus Homomorphism with Cancellable Codomain Preserves Identity can be applied.
$\blacksquare$
Sources
- 1965: J.A. Green: Sets and Groups ... (previous) ... (next): $\S 7.2$. Some lemmas on homomorphisms: Lemma $\text{(ii)}$
- 1965: Seth Warner: Modern Algebra ... (previous) ... (next): Chapter $\text {II}$: New Structures from Old: $\S 12$: Homomorphisms: Theorem $12.3: \ 3^\circ$
- 1966: Richard A. Dean: Elements of Abstract Algebra ... (previous) ... (next): $\S 1.10$: Theorem $22$