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Exercise 2219Algebra › Rings and fieldsM1Added 3 Nov 2026

The spectrum of a ring (statement)

#spectrum#prime ideals#Zariski topology

Statement

Define the spectrum Spec⁡(R)\operatorname{Spec}(R) of a commutative ring RR and compute it for R=ZR=\mathbb{Z}.

Hint

Spec⁡(R)\operatorname{Spec}(R) is the set of prime ideals of RR, equipped with the Zariski topology.

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Solution

Definition. Spec⁡(R)={p⊆R:p prime ideal}\operatorname{Spec}(R)=\{\mathfrak{p}\subseteq R:\mathfrak{p}\text{ prime ideal}\}.

Zariski topology. Closed sets are V(I)={p:p⊇I}V(I)=\{\mathfrak{p}:\mathfrak{p}\supseteq I\} for ideals I⊆RI\subseteq R.

Example. Spec⁡(Z)={(0)}∪{(p):p prime}\operatorname{Spec}(\mathbb{Z})=\{(0)\}\cup\{(p):p\text{ prime}\}.

Topological structure. The point (0)(0) is the generic point, dense in Spec⁡(Z)\operatorname{Spec}(\mathbb{Z}). The points (p)(p) are closed.

Conclusion. Spec⁡(Z)\operatorname{Spec}(\mathbb{Z}) consists of the zero ideal and the prime ideals (p)(p), with Zariski topology where (0)(0) is dense and each (p)(p) is a closed point.