Image of Preimage of Subring under Ring Epimorphism
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Theorem
Let $\phi: \struct {R_1, +_1, \circ_1} \to \struct {R_2, +_2, \circ_2}$ be a ring epimorphism.
Let $S_2$ be a subring of $R_2$.
Then:
- $\phi \sqbrk {\phi^{-1} \sqbrk {S_2} } = S_2$
Proof
As $\phi$ is an epimorphism, it is a surjection, and so $\Img \phi = R_2$.
So $S_2 \subseteq \Img {R_1}$.
The result then follows from Image of Preimage under Mapping.
$\blacksquare$
Sources
- 1965: Seth Warner: Modern Algebra ... (previous) ... (next): Chapter $\text {IV}$: Rings and Fields: $22$. New Rings from Old: Theorem $22.6: \ 3^\circ$