# Prüfer ring

Definition.  A commutative ring $R$ with non-zero unity is a Prüfer ring (cf. Prüfer domain) if every finitely generated    regular ideal of $R$ is invertible. (It can be proved that if every ideal of $R$ generated by two elements is invertible, then all finitely generated ideals are invertible; cf. invertibility of regularly generated ideal.)

Theorem 1 (Pahikkala 1982).  Let $R$ be a commutative ring with non-zero unity and let $T$ be the total ring of fractions of $R$.  Then, $R$ is a Prüfer ring iff the equation

 $\displaystyle\mathfrak{m}_{f}\mathfrak{m}_{g}=\mathfrak{m}_{fg}$ (1)

holds whenever $f$ and $g$ belong to the polynomial ring $T[x]$ and at least one of the fractional ideals $\mathfrak{m}_{f}$ and $\mathfrak{m}_{g}$ is . (See also product of finitely generated ideals.)

Theorem 2 (Pahikkala 1982).   The commutative ring $R$ with non-zero unity is Prüfer ring iff the multiplication rule

 $(a,\,b)(c,\,d)=(ac,\,ad+bc,\,bd)$

for the integral ideals of $R$ holds whenever at least one of the generators   $a$, $b$, $c$ and $d$ is not zero divisor  .

The proofs are found in the paper

J. Pahikkala 1982: “Some formulae for multiplying and inverting ideals”.  – Annales universitatis turkuensis 183. Turun yliopisto (University of Turku).

Cf. the entries “multiplication rule gives inverse ideal (http://planetmath.org/MultiplicationRuleGivesInverseIdeal)” and “two-generator property (http://planetmath.org/TwoGeneratorProperty)”.

An additional characterization of Prüfer ring is found here in the entry “least common multiple   (http://planetmath.org/LeastCommonMultiple)”, several other characterizations in  (p. 238–239).

Note.  A commutative ring $R$ satisfying the equation (1) for all polynomials $f,\,g$ is called a Gaussian ring.  Thus any Prüfer domain (http://planetmath.org/PruferDomain) is always a Gaussian ring, and conversely (http://planetmath.org/Converse), an integral domain  , which is a Gaussian ring, is a Prüfer domain.  Cf. .

## References

• 1 M. Larsen & P. McCarthy: Multiplicative theory of ideals.  Academic Press. New York (1971).
• 2 Sarah Glaz: “The weak dimensions of Gaussian rings”. – Proc. Amer. Math. Soc. (2005).
 Title Prüfer ring Canonical name PruferRing Date of creation 2015-05-05 15:21:07 Last modified on 2015-05-05 15:21:07 Owner pahio (2872) Last modified by pahio (2872) Numerical id 89 Author pahio (2872) Entry type Theorem Classification msc 13C13 Classification msc 13F05 Related topic LeastCommonMultiple Related topic GeneratorsOfInverseIdeal Related topic ProductOfIdeals Related topic MultiplicationRing Related topic PruferDomain Related topic InvertibilityOfRegularlyGeneratedIdeal Related topic MultiplicationRuleGivesInverseIdeal Related topic ContentOfPolynomial Related topic ProductOfFinitelyGeneratedIdeals Defines Prüfer ring Defines coefficient module Defines Gaussian ring