In mathematics, a Prüfer domain is a type of commutative ring that generalizes Dedekind domains in a non-Noetherian context. These rings possess the nice ideal and module theoretic properties of Dedekind domains, but usually only for finitely generated modules. Prüfer domains are named after the German mathematician Heinz Prüfer. Examples The ring of entire functions on the open complex plane form a Prüfer domain. The ring of integer valued polynomials with rational coefficients is a Prüfer domain, although the ring of integer polynomials is not . While every number ring is a Dedekind domain, their union, the ring of algebraic integers, is a Prüfer domain. Just as a Dedekind domain is locally a discrete valuation ring, a Prüfer domain is locally a valuation ring, so that Prüfer domains act as non-noetherian analogues of Dedekind domains. Indeed, a domain that is the direct limit of subrings that are Prüfer domains is a Prüfer domain . Many Prüfer domains are also Bézout domains, that is, not only are finitely generated ideals projective, they are even free (that is, principal). For instance the ring of analytic functions on any non-compact Riemann surface is a Bézout domain , and the ring of algebraic integers is Bézout. Definitions A Prüfer domain is a semihereditary integral domain. Equivalently, a Prüfer domain may be defined as a commutative ring without zero divisors in which every non-zero finitely generated ideal is invertible. Many different characterizations of Prüfer domains are known. Bourbaki lists fourteen of them, has around forty, and open with nine. As a sample, the following conditions on an integral domain R are equivalent to R being a Prüfer domain, i.e. every finitely generated ideal of R is projective: Ideal arithmetic Every non-zero finitely generated ideal I of R is invertible: i.e. , where and is the field of fractions of R. Equivalently, every non-zero ideal generated by two elements is invertible. For any (finitely generated) non-zero ideals I, J, K of R, the following distributivity property holds: For any (finitely generated) ideals I, J, K of R, the following distributivity property holds: For any (finitely generated) non-zero ideals I, J of R, the following property holds: For any finitely generated ideals I, J, K of R, if IJ = IK then J = K or I = 0. Localizations For every prime ideal P of R, the localization RP of R at P is a valuation