arXiv subjects

Muhammad Zafrullah

Publications and source records attributed to Muhammad Zafrullah.

At least 19 recordsLinked to original sources

arXiv2022

On Chevalley's Extension Theorem

Professor Daniel Anderson informed me, recently, that there is an error in the proof of Theorem 56 of Kaplansky's book on Commutative Rings. His (Dan's) reason was "He (Kaplansky) orders by reverse inclusion but in the last line uses inclusion, so we don't contradict maximality (which is minimality)". The aim of this short note is to indicate that while Dan Anderson appears to be correct in pointing out an error in the proof of Theorem 56 of the above mentioned book, the statement of the theorem is a correct consequence of a Theorem of Chevalley.

math.AC↗

arXiv2022

Condensed domains and the $D+XL[X]$ construction

Let $D$ be an integral domain with quotient field $K$ and let $\mathcal{I}% (D) $ be the set of nonzero ideals of $D$. Call, for $I,J\in \mathcal{I}(D)$ , the product $IJ$ of ideals condensed if $IJ=\{ij|i\in I,j\in J\}.$ Call $D$ a condensed domain if for each pair $I,J$ the product $IJ$ is condensed. We show that if $a,b$ are elements of a condensed domain such that $aD\cap bD=abD,$ then $(a,b)=D.$ It was shown in [Comm. Algebra 15 (1987), 1895-1920] that a pre-Schreier domain is a $\ast $-domain, i.e., $D$ satisfies $\ast :$ For every pair $\{a_{i}\}_{i=1}^{m},\{b_{j}\}_{j=1}^{n}$ of sets of nonzero elements of $D$ we have $(\cap (a_{i}))(\cap b_{j})=\cap (a_{i}b_{j}).$ We show that a condensed domain $D$ is pre-Schreier if and only if $D$ is a $ \ast $-domain. We also show that if $A\subseteq B$ is an extension of domains and $A+XB[X]$ is condensed, then $B$ must be a field and $A$ must be condensed and in this case $[B:K]<4.$ In particular we study the necessary and sufficient conditions for $D+XL[X]$ to be condensed, where $D$ is a domain and $L$ an extension field of $K.$ It may be noted that if $D$ is not a field $D[X]$ is never condensed. So for $D$ condensed $D+XK[X]$ is a way of constructing new condensed domains from old

math.AC↗

arXiv2022

Integral domains and the IDF property

An integral domain $D$ is called an irreducible-divisor-finite domain (IDF-domain) if every nonzero element of $D$ has finitely many irreducible divisors up to associates. The study of IDF-domains dates back to the seventies. In this paper, we investigate various aspects of the IDF property. In 2009, P.~Malcolmson and F. Okoh proved that the IDF property does not ascend from integral domains to their corresponding polynomial rings, answering a question posed by D. D. Anderson, D. F. Anderson, and the second author two decades before. Here we prove that the IDF property ascends in the class of PSP-domains, generalizing the known result (also by Malcolmson and Okoh) that the IDF property ascends in the class of GCD-domains. We put special emphasis on IDF-domains where every nonunit is divisible by an irreducible, which we call TIDF-domains, and we also consider PIDF-domains, which form a special class of IDF-domains introduced by Malcolmson and Okoh in 2006. We investigate both the TIDF and the PIDF properties under taking polynomial rings and localizations. We also delve into their behavior under monoid domain and $D+M$ constructions

math.AC↗

arXiv2021

Riesz and pre-Riesz monoids

Call a directed partially ordered cancellative divisibility monoid $M$ a Riesz monoid if for all $x,y_{1},y_{2}\geq 0$ in $M,$ $x\leq y_{1}+y_{2}\Rightarrow x=x_{1}+x_{2}$ where $0\leq x_{i}\leq y_{i}$. We explore the necessary and sufficient conditions under which a Riesz monoid $% M $ with $M^{+}=\{x\geq 0|x\in M\}=M$ generates a Riesz group and indicate some applications. We call a directed p.o. monoid $M$ $\Pi $-pre-Riesz if $% M^{+}=M$ and for all $x_{1},x_{2},...,x_{n}\in M$, $% glb(x_{1},x_{2},...,x_{n})=0$ or there is $r\in \Pi $ such that $0<r\leq x_{1},x_{2},...,x_{n},$ for some subset $\Pi $ of $M.$ We explore examples of $\Pi $-pre-Riesz monoids of $\star $-ideals of different types. We show for instance that if $M$ is the monoid of nonzero (integral) ideals of a Noetherian domain $D$ and $\Pi $ the set of invertible ideals, $M$ is $\Pi $ -pre-Riesz if and only $D$ is a Dedekind domain. We also study factorization in pre-Riesz monoids of a certain type and link it with factorization theory of ideals in an integral domain.

math.AC↗

arXiv2021

Revisiting G-Dedekind domains

Let $R$ be an integral domain with $qf(R)=K$ and let $F(R)$ be the set of nonzero fractional ideals of $R.$ Call $R$ a dually compact domain (DCD) if for each $I\in F(R)$ the ideal $I_{v}=(I^{-1})^{-1}$ is a finite intersection of principal fractional ideals. We characterize DCDs and show that the class of DCDs properly contains various classes of integral domains, such as Noetherian, Mori and Krull domains. In addition we show that a Schreier DCD is a GCD domain with the property that for each $A\in F(R)$ the ideal $A_{v}$ is principal. We show that a domain $R$ is G-Dedekind domain (i.e. has the property that $A_{v}$ is invertible for each $A\in F(R)$) if and only if $R$ is a DCD satisfying the property $\ast :$ for all pairs of subsets $\{a_{1},...,a_{m}\},\{b_{1},...b_{n}\}\subseteq K\backslash \{0\},$ $(\cap _{i=1}^{m}(a_{i})(\cap _{j=1}^{n}(b_{j}))=\cap _{i,j=1}^{m,n}a_{i}b_{j}$. We discuss what the appropriate name for G-Dedekind domains and related notions should be. We also make some observations about how the DCDs behave under localizations and polynomial ring extensions.

math.AC↗

arXiv2021

On super $v$-domains

An integral domain $D,$ with quotient field $K,$ is a $v$-domain if for each nonzero finitely generated ideal $A$ of $D$ we have $(AA^{-1})^{-1}=D.$ It is well known that if $D$ is a $v$-domain$,$ then some quotient ring $D_{S}$ of $D$ may not be a $v$-domain. Calling $D$ a super $v$-domain if every quotient ring of $D$ is a $v$-domain we characterize super $v$-domains as locally $v$-domains. Using techniques from factorization theory we show that $D$ is a super $v$-domain if and only if $D[X]$ is a super $v$-domain if and only if $D+XK[X]$ is a super $v$-domain and give new examples of super $v$ -domains that are strictly between $v$-domains and P-domains that were studied in [Manuscripta Math. 35(1981)1-26]

math.AC↗

arXiv2020

Semirigid GCD domains II

Let $D$ be an integral domain with quotient field $K,$ throughout$.$ Call two elements $x,y\in D\backslash \{0\}$ $v$-coprime if $xD\cap yD=xyD.$ Call a nonzero non unit $r$ of an integral domain $D$ rigid if for all $x,y|r$ we have $x|y$ or $y|x.$ Also call $D$ semirigid if every nonzero non unit of $D$ is expressible as a finite product of rigid elements. We show that a semirigid domain $D$ is a GCD domain if and only if $D$ satisfies $\ast :$ product of every pair of non-$v$-coprime rigid elements is again rigid. Next call $a\in D$ a valuation element if $aV\cap D=aD$ for some valuation ring $% V $ with $D\subseteq V\subseteq K$ and call $D$ a VFD if every nonzero non unit of $D$ is a finite product of valuation elements. It turns out that a valuation element is what we call a packed element: a rigid element $r$ all of whose powers are rigid and $\sqrt{rD}$ is a prime ideal. Calling $D$ a semi packed domain (SPD) if every nonzero non unit of $D$ is a finite product of packed elements, we study SPDs and explore situations in which an SPD is a semirigid GCD domain.

math.AC↗

arXiv2020

Domains whose ideals meet a universal restriction

Let $S(D)$ represent a set of proper nonzero ideals $I(D)$ (resp., $t$ -ideals $I_{t}(D)$) of an integral domain $D\neq qf(D)$ and let $P$ be a valid property of ideals of $D.$ We say $S(D)$ meets $P$ (denoted $ S(D)\vartriangleleft P)$ if each $s\in S(D)$ is contained in an ideal satisfying $P$. If $S(D)$ $\vartriangleleft P,$ $\dim (D)$ can't be controlled. When $R=D[X],$ $I(D)$ $\vartriangleleft P$ does not imply $I(R)$ $\vartriangleleft P$ while $I_{t}(D)$ $\vartriangleleft P$ implies $I_{t}(R)$ $\vartriangleleft P$ usually. We say $S(D)$ meets $P$ with a twist $($ written $S(D)\vartriangleleft ^{t}P)$ if each $s\in S(D)$ is such that, for some $n\in N,$ $s^{n}$ is contained in an ideal satisfying $P$ and study $ S(D)\vartriangleleft ^{t}P,$ as its predecessor. A modification of the above approach is used to give generalizations of Almost Bezout domains.

math.AC↗

arXiv2019

Almost discrete valuation domains

Let $D$ be an integral domain. Then $D$ is an almost valuation (AV-)domain if for $a, b\in D\setminus \{0\}$ there exists a natural number $n$ with $a^{n}\mid b^{n}$ or $b^{n}\mid a^{n}$. AV-domains are closely related to valuation domains, for example, $D$ is an AV-domain if and only if the integral closure $\bar{D}$ is a valuation domain and $D\subseteq \bar{D}$ is a root extension. In this note we explore various generalizations of DVRs (which we might call almost DVRs) such as Noetherian AV-domains, AV-domains with $\bar{D}$ a DVR, and quasilocal and local API-domains (i.e., for $\{a_{\alpha}\}_{\alpha\in \Lambda}\subseteq D$, there exists an $n$ with $(\{a_{\alpha}^{n}\}_{\alpha\in \Lambda})$ principal). The structure of complete local AV-domains and API-domains is determined.

math.AC↗

arXiv2019

Two generalizations of Krull domains

In this paper we introduce two new generalizations of Krull domains: $\ast$-almost independent rings of Krull type ($\ast$-almost IRKTs) and $\ast$-almost generalized Krull domains ($\ast$-AGKDs), neither of which need be integrally closed. We characterize them using certain types of $\ast$-homogeneous ideals. To do this we introduce $\ast$-almost super-homogeneous ideals and $\ast$-almost super-SH domains. We prove that a domain $D$ is a $\ast$-almost IRKT if and only if $D$ is a $\ast$-almost super-SH domain and that a domain is a $\ast$-AGKD if and only if $D$ is a type 1 $\ast$-almost super-SH domain. Further, we study $\ast$-almost factorial general-SH domains ($\ast$-afg SH domains) and we prove that a domain $D$ is a $\ast$-afg-SH domain if and only if $D$ is a $\ast$-IRKT and an AGCD-domain.

math.AC↗

arXiv2019

On $\ast$-homogeneous ideals

Let $\ast $ be a star operation of finite character. Call a $\ast $-ideal $I$ of finite type a $\ast $-homogeneous ideal if $I$ is contained in a unique maximal $\ast $-ideal $M=M(I).$ A maximal $\ast $-ideal that contains a $\ast $-homogeneous ideal is called $\ast $-potent and the same name bears a domain all of whose maximal $\ast $-ideals are $\ast $-potent. One among the various aims of this article is to indicate what makes a $\ast $-ideal of finite type a $\ast $-homogeneous ideal, where and how we can find one, what they can do and how this notion came to be. We also prove some results of current interest in ring theory using some ideas from this author's joint work in \cite{LYZ 2014} on partially ordered monoids. For example we characterize when a commutative Riesz monoid generates a Riesz group.

math.AC↗

arXiv2018

$t$-local domains and valuation domains

In a valuation domain $(V,M)$ every nonzero finitely generated ideal $J$ is principal and so, in particular, $J=J^t$, hence the maximal ideal $M$ is a $t$-ideal. Therefore, the $t$-local domains (i.e., the local domains, with maximal ideal being a $t$-ideal) are "cousins" of valuation domains, but, as we will see in detail, not so close. Indeed, for instance, a localization of a $t$-local domain is not necessarily $t$-local, but of course a localization of a valuation domain is a valuation domain. So it is natural to ask under what conditions is a $t$-local domain a valuation domain? The main purpose of the present paper is to address this question, surveying in part previous work by various authors containing useful properties for applying them to our goal.

math.AC↗

arXiv2018

On $\ast $-Semi Homogeneous Domains

Let $\ast $ be a finite character star operation defined on an integral domain $D.$ Call a nonzero $\ast $-ideal $I$ of finite type a $\ast $ -homogeneous ($\ast $-homog) ideal, if $I\subsetneq D$ and $(J+K)^{\ast }\neq D$ for every pair $D\supsetneq J,K\supseteq I$ of proper $\ast $ -ideals of finite type$.$ Call an integral domain $D$ a $\ast $-Semi Homogeneous Domain ($\ast $-SHD) if every proper principal ideal $xD$ of $D$ is expressible as a $\ast $-product of finitely many $\ast $-homog ideals. We show that a $\ast $-SHD contains a family $\mathcal{F}$ of prime ideals such that (a) $D=\cap_{P\in \mathcal{F}}D_{P},$ a locally finite intersection and (b) no two members of $\mathcal{F}$ contain a common non zero prime ideal. The $\ast $-SHDs include h-local domains, independent rings of Krull type, Krull domains, UFDs etc. We show also that we can modify the definition of the $\ast $-homog ideals to get a theory of each special case of a $\ast $-SH domain.

math.AC↗

arXiv2017

$\star $-super potent domains

For a finite-type star operation $\star$ on a domain $R$, we say that $R$ is $\star$-super potent if each maximal $\star$-ideal of $R$ contains a finitely generated ideal $I$ such that (1) $I$ is contained in no other maximal $\star$-ideal of $R$ and (2) $J$ is $\star$-invertible for every finitely generated ideal $J \supseteq I$. Examples of $t$-super potent domains include domains each of whose maximal $t$-ideals is $t$-invertible (e.g., Krull domains). We show that if the domain $R$ is $\star$-super potent for some finite-type star operation $\star$, then $R$ is $t$-super potent, we study $t$-super potency in polynomial rings and pullbacks, and we prove that a domain $R$ is a generalized Krull domain if and only if it is $% t $-super potent and has $t$-dimension one.

math.AC↗

arXiv2017

On $\star $-Power Conductor domains

Let $D$ be an integral domain and $\star $ a star operation defined on $D$. We say that $D$ is a $\star $-power conductor domain ($\star $-PCD) if for each pair $a,b\in D\backslash (0)$ and for each positive integer $n$ we have $Da^{n}\cap Db^{n}=((Da\cap Db)^{n})^{\ast }.$ We study $\star $-PCDs and characterize them as root closed domains satisfying $ ((a,b)^{n})^{-1}=(((a,b)^{-1})^{n})^{\star }$ for all nonzero $a,b$ and all natural numbers $n\geq 1$. From this it follows easily that Pr\"{u}fer domains are $d$-PCDs (where $d$ denotes the trivial star operation), and $v$ -domains (e.g., Krull domains) are $v$-PCDs, thereby establishing that a $v$ -domain (e.g., a Prufer or Krull domain) is a $\star $ -PCD. We also consider when a $\star $-PCD is completely integrally closed, and this leads to new characterizations of Krulll domains. In particular, we show that a Noetherian domain is a Krull domain if and only if it is a $w$ -PCD.

math.AC↗

arXiv2009

On $v$-domains: a survey

An integral domain $D$ is a $v$--domain if, for every finitely generated nonzero (fractional) ideal $F$ of $D$, we have $(FF^{-1})^{-1}=D$. The $v$--domains generalize Prüfer and Krull domains and have appeared in the literature with different names. This paper is the result of an effort to put together information on this useful class of integral domains. In this survey, we present old, recent and new characterizations of $v$--domains along with some historical remarks. We also discuss the relationship of $v$--domains with their various specializations and generalizations, giving suitable examples.

math.AC↗

arXiv2009

A "$v$-operation free" approach to Prüfer $v$-multiplication domains

The so called Prüfer $v$-multiplication domains (P$v$MD's) are usually defined as domains whose finitely generated nonzero ideals are $t$-invertible. These domains generalize Prüfer domains and Krull domains. The P$v$MD's are relatively obscure compared to their very well known special cases. One of the reasons could be that the study of P$v$MD's uses the jargon of star operations, such as the $v$-operation and the $t$-operation. In this paper, we provide characterizations of and basic results on P$v$MD's and related notions without star operations.

math.AC↗

arXiv2008

On $v$--domains and star operations

Let $\ast$ be a star operation on an integral domain $D$. Let $\f(D)$ be the set of all nonzero finitely generated fractional ideals of $D$. Call $D$ a $\ast$--Prüfer (respectively, $(\ast, v)$--Prüfer) domain if $(FF^{-1})^{\ast}=D$ (respectively, $(F^vF^{-1})^{\ast}=D$) for all $F\in \f(D)$. We establish that $\ast$--Prüfer domains (and $(\ast, v)$--Prüfer domains) for various star operations $\ast $ span a major portion of the known generalizations of Prüfer domains inside the class of $v$--domains. We also use Theorem 6.6 of the Larsen and McCarthy book [Multiplicative Theory of Ideals, Academic Press, New York--London, 1971], which gives several equivalent conditions for an integral domain to be a Prüfer domain, as a model, and we show which statements of that theorem on Prüfer domains can be generalized in a natural way and proved for $\ast$--Prüfer domains, and which cannot be. We also show that in a $\ast $--Prüfer domain, each pair of $\ast $-invertible $\ast $-ideals admits a GCD in the set of $\ast $-invertible $\ast $-ideals, obtaining a remarkable generalization of a property holding for the "classical" class of Prüfer $v$--multiplication domains. We also link $D$ being $\ast $--Prüfer (or $(\ast, v)$--Prüfer) with the group Inv$^{\ast}(D)$ of $\ast $-invertible $\ast $-ideals (under $\ast$-multiplication) being lattice-ordered.

math.AC↗