Definition:Generated Ring Extension
Definition
Let $S$ be a commutative rings with unity.
Let $R$ be a subring of $S$ with unity such that the unity of $R$ is the unity of $S$.
That is, $S$ is a ring extension of $R$.
Let $T \subseteq S$ be a subset of $S$.
Definition 1
The ring extension $R \sqbrk T$ generated by $T$ is the smallest subring of $S$ containing $T$ and $R$, that is, the intersection of all subrings of $S$ containing $T$ and $R$.
Thus $T$ is a generator of $R \sqbrk T$ if and only if $R \sqbrk T$ has no proper subring containing $T$ and $R$.
Definition 2
Let $R \sqbrk {\set {X_t} }$ be the polynomial ring in $T$ variables $X_t$.
Let $\operatorname {ev} : R \sqbrk {\set {X_t} } \to S$ be the evaluation homomorphism associated with the inclusion $T \hookrightarrow S$.
The ring extension $R \sqbrk T$ generated by $T$ is $\Img {\operatorname {ev} }$, the image of $\operatorname {ev}$.
$T$ is said to be a generator of $R \sqbrk T$.
Also see
- Equivalence of Definitions of Generated Ring Extension
- Definition:Generated Field Extension
- Definition:Generated Subalgebra over Ring
Sources
- Weisstein, Eric W. "Extension Ring." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ExtensionRing.html