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Marco Fontana

Publications and source records attributed to Marco Fontana.

47 records · Page 3Linked to original sources
arXiv2005

On the Star Class Group of a Pullback

For the domain $R$ arising from the construction $T, M,D$, we relate the star class groups of $R$ to those of $T$ and $D$. More precisely, let $T$ be an integral domain, $M$ a nonzero maximal ideal of $T$, $D$ a proper subring of $k:=T/M$, $ϕ: T\to k$ the natural projection, and let $R=ϕ^{-1}(D)$. For each star operation $\ast$ on $R$, we define the star operation $\ast_ϕ$ on $D$, i.e., the ``projection'' of $\ast$ under $ϕ$, and the star operation ${(\ast)}_{_{T}}$ on $T$, i.e., the ``extension'' of $\ast$ to $T$. Then we show that, under a mild hypothesis on the group of units of $T$, if $\ast$ is a star operation of finite type, $0\to \Cl^{\ast_ϕ}(D) \to \Cl^\ast(R) \to \Cl^{{(\ast)}_{_{T}}}(T)\to 0$ is split exact. In particular, when $\ast = t_{R}$, we deduce that the sequence $ 0\to \Cl^{t_{D}}(D) {\to} \Cl^{t_{R}}(R) {\to}\Cl^{(t_{R})_{_{T}}}(T) \to 0 $ is split exact. The relation between ${(t_{R})_{_{T}}}$ and $t_{T}$ (and between $\Cl^{(t_{R})_{_{T}}}(T)$ and $\Cl^{t_{T}}(T)$) is also investigated.

math.AC↗
arXiv2004

Semistar invertibility on integral domains

After the introduction in 1994, by Okabe and Matsuda, of the notion of semistar operation, many authors have investigated different aspects of this general and powerful concept. A natural development of the recent work in this area leads to investigate the concept of invertibility in the semistar setting. In this paper, we will show the existence of a ``theoretical obstruction'' for extending many results, proved for star-invertibility, to the semistar case. For this reason, we will introduce two distinct notions of invertibility in the semistar setting (called $\star$--invertibility and quasi--$\star$--invertibility), we will discuss the motivations of these ``two levels'' of invertibility and we will extend, accordingly, many classical results proved for the $d$--, $v$--, $t$-- and $w$-- invertibility.

math.AC↗
arXiv2004

Integral Domains whose Simple Overrings are Intersections of Localizations

Call a domain $R$ an sQQR-domain if each simple overring of $R$, i.e., each ring of the form $R[u]$ with $u$ in the quotient field of $R$, is an intersection of localizations of $R$. We characterize Prüfer domains as integrally closed sQQR-domains. In the presence of certain finiteness conditions, we show that the sQQR-property is very strong; for instance, a Mori sQQR-domain must be a Dedekind domain. We also show how to construct sQQR-domains which have (non-simple) overrings which are not intersections of localizations.

math.AC↗
arXiv2004

Semistar Dedekind Domains

Let $D$ be an integral domain and $\star$ a semistar operation on $D$. As a generalization of the notion of Noetherian domains to the semistar setting, we say that $D$ is a $\star$--Noetherian domain if it has the ascending chain condition on the set of its quasi--$\star$--ideals. On the other hand, as an extension the notion of Prüfer domain (and of Prüfer $v$--multiplication domain), we say that $D$ is a Prüfer $\star$--multiplication domain (P$\star$MD, for short) if $D_M$ is a valuation domain, for each quasi--$\star_{_{f}}$--maximal ideal $M$ of $D$. Finally, recalling that a Dedekind domain is a Noetherian Prüfer domain, we define a $\star$--Dedekind domain to be an integral domain which is $\star$--Noetherian and a P$\star$MD. In the present paper, after a preliminary study of $\star$--Noetherian domains, we investigate the $\star$--Dedekind domains. We extend to the $\star$--Dedekind domains the main classical results and several characterizations proven for Dedekind domains. In particular, we obtain a characterization of a $\star$--Dedekind domain by a property of decomposition of any semistar ideal into a ``semistar product'' of prime ideals. Moreover, we show that an integral domain $D$ is a $\star$--Dedekind domain if and only if the Nagata semistar domain Na$(D, \star)$ is a Dedekind domain. Several applications of the general results are given for special cases of the semistar operation $\star$.

math.AC↗
arXiv2003

Star operations and Pullbacks

In this paper we study the star operations on a pullback of integral domains. In particular, we characterize the star operations of a domain arising from a pullback of ``a general type'' by introducing new techniques for ``projecting'' and ``lifting'' star operations under surjective homomorphisms of integral domains. We study the transfer in a pullback (or with respect to a surjective homomorphism) of some relevant classes or distinguished properties of star operations such as $v-, t-, w-, b-, d-,$ finite type, e.a.b., stable, and spectral operations. We apply part of the theory developed here to give a complete positive answer to a problem posed by D. F. Anderson in 1992 concerning the star operations on the ``$D+M$'' constructions.

math.AC↗
arXiv2003

Semistar linkedness and flatness, Prüfer semistar multiplication domains

In 1994, Matsuda and Okabe introduced the notion of semistar operation, extending the "classical" concept of star operation. In this paper, we introduce and study the notions of semistar linkedness and semistar flatness which are natural generalizations, to the semistar setting, of their corresponding "classical" concepts. As an application, among other results, we obtain a semistar version of Davis' and Richman's overring-theoretical theorems of characterization of Prüfer domains for Prüfer semistar multiplication domains.

math.AC↗
arXiv2003

Local--Global Properties for Semistar Operations

We study the "local" behavior of several relevant properties concerning semistar operations, like finite type, stable, spectral, e.a.b. and a.b. We deal with the "global" problem of building a new semistar operation on a given integral domain, by "gluing" a given homogeneous family of semistar operations defined on a set of localizations. We apply these results for studying the local--global behavior of the semistar Nagata ring and the semistar Kronecker function ring. We prove that an integral domain $D$ is a Pr{ü}fer $\star$--multiplication domain if and only if all its localizations $D_{P}$ are Pr{ü}fer $\star_P$--multiplication domains.

math.AC↗
arXiv2003

Nagata Rings, Kronecker Function Rings and Related Semistar Operations

In 1994, Matsuda and Okabe introduced the notion of semistar operation. This concept extends the classical concept of star operation (cf. for instance, Gilmer's book \cite{G}) and, hence, the related classical theory of ideal systems based on the works by W. Krull, E. Noether, H. Prüfer and P. Lorenzen from 1930's. In \cite{FL1} and \cite{FL2} the current authors investigated properties of the Kronecker function rings which arise from arbitrary semistar operations on an integral domain $D$. In this paper we extend that study and also generalize Kang's notion of a star Nagata ring \cite{Kang:1987} and \cite{Kang:1989} to the semistar setting. Our principal focuses are the similarities between the ideal structure of the Nagata and Kronecker semistar rings and between the natural semistar operations that these two types of function rings give rise to on $D$.

math.AC↗
arXiv2002

Prüfer $\star$--multiplication domains and semistar operations

We prove a characterization of a P$\star$MD, when $\star$ is a semistar operation, in terms of polynomials (by using the classical characterization of Prüfer domains, in terms of polynomials given by R. Gilmer and J. Hoffman \cite{Gilmer/Hoffmann:1974}, as a model), extending a result proved in the star case by E. Houston, S.J. Malik and J. Mott \cite{Houston/Malik/Mott:1984}. We also deal with the preservation of the P$\star$MD property by ``ascent'' and ``descent'' in case of field extensions. In this context, we generalize to the P$\star$MD case some classical results concerning Prüfer domains and P$v$MDs. In particular, we reobtain as a particular case a result due to H. Prüfer \cite{Prufer} and W. Krull \cite{Krull:1936} (cf. also F. Lucius \cite{Lucius:1998} and F. Halter-Koch \cite{Koch:2000}). Finally, we develop several examples and applications when $\star$ is a (semi)star given explicitly (e.g. we consider the case of the ``standard'' $v$--, $t$--, $b$--, $w$--operations or the case of semistar operations associated to appropriate families of overrings).

math.AC↗