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Acorn Domains

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Acorn Domains
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  • Title: "Acorn Domains: A Concise Overview"
  • Definition
  • Basic properties
  • Examples
  • Applications
  • References
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Acorn Domains

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Acorn Domains

In commutative algebra a one‑dimensional local ring whose only non‑zero prime ideals are maximal is called an acorn domain. Its spectrum consists of a minimal point (0) and a single closed point determined by the maximal ideal.

Basic Properties

  • Every acorn domain is integrally closed; its localization at the maximal ideal is a discrete valuation ring (DVR).
  • If Noetherian it is a Dedekind domain with a single non‑zero prime.
  • Global homological dimension is one; thus all finitely generated torsion‑free modules are projective and every invertible ideal is principal.

Examples

  • For a field $K$, $K[[t]]_{(t)}$ is an acorn domain: the maximal ideal $(t)$ is the only non‑zero prime.
  • Localizing the integer ring at a single prime, $ \mathbb{Z}_{(p)}$, is a DVR and hence an acorn domain.

Applications

  • Local rings of smooth points on algebraic curves are DVRs, providing the standard local model for intersection theory.
  • In algebraic number theory, localizations of rings of integers at a prime give acorn domains, simplifying local class‑field calculations.

Acorn Domains

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In commutative algebra a one‑dimensional local ring whose only non‑zero prime ideals are maximal is called an acorn domain. Its spectrum consists of a minimal point (0) and a single closed point determined by the maximal ideal.

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Basic Properties

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    Examples

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      Applications

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        References

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          Acorn Domains

          In commutative algebra a one‑dimensional local ring whose only non‑zero prime ideals are maximal is called an acorn domain. Its spectrum consists of a minimal point (0) and a single closed point determined by the maximal ideal.

          Basic Properties

          • Every acorn domain is integrally closed; localizing at its unique maximal ideal gives a discrete valuation ring (DVR).
  • In the Noetherian case it is a Dedekind domain with a single non‑zero prime.
  • Global homological dimension is one: every finitely generated torsion‑free module is projective and every invertible ideal is principal.

Examples

  • For a field \(K\), \(K[[t]]_{(t)}\) is an acorn domain: the maximal ideal \((t)\) is the only non‑zero prime.
  • Localizing the integer ring at a prime, \(\mathbb{Z}_{(p)}\), is a DVR and hence an acorn domain.

Applications

  • Local rings of smooth points on algebraic curves are DVRs, providing the standard local model for intersection theory.
  • Localizations of rings of integers at a single prime give acorn domains, simplifying local class‑field calculations.

References

  • Kaplansky, I. Commutative Rings, 1974.
  • Atiyah & Macdonald, Introduction to Commutative Algebra, 1969.
  • Bruns & Herzog, Cohen–Macaulay Rings, 1998.

References & Further Reading

  • Kaplansky, I. Commutative Rings, 1974.
  • Atiyah & Macdonald, Introduction to Commutative Algebra, 1969.
  • Bruns & Herzog, Cohen–Macaulay Rings, 1998.
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