bluuebunny/crossref_metadata_2025 huggingface dataset:
Minimal line graphs
Authors: Sumner David P.
Published: May 2009

In this paper all graphs will be ordinary graphs, i.e. finite, undirected, and without loops or multiple edges. For points x and y of a graph G, we shall indicate that x is adjacent to y by writing x ⊥ y, and if x is not adjacent to y we shall write xy. We shall denote the degree of a point x by δ(x) and the minimal degree of G by δ(G).

By the line graph of a graph G we shall mean the graph L(G) whose points are the edges of G, with two points of L(G) adjacent whenever they are adjacent in G. A graph G is said to be a line graph if there exists a graph H such that G = L(H).
A test for commutators
Authors: Liebeck Hans
Published: May 2009

In the course of a study of commutator subgroups I. D. Macdonald [1] presented the free nilpotent group G4 of class 2 on 4 generators as an example of a nilpotent group whose commutator subgroup has elements that are not commutators. To demonstrate this he proceeded as follows: let G4 = 〈a1, a2, a3, a4〉 and put cij = [ai, aj] for 1 ≦ i < j ≦ 4. Then the relations in G4 are [cij, ak] = 1 for 1 ≦ i < j ≦ 4 and 1 ≦ k ≦ 4, and their consequences. Macdonald observed that an arbitrary commutator may be written as

which simplifies to

where δij = αiβj - αjβi The indices δij satisfy the relation

It follows that the element c13c24 in G′4 (for which δ12 = δ14 = δ23 = δ34 = 0 and δ13 = δ24 = 1) is not a commutator.
The convolution x-r*xs
Authors: Fisher B.
Published: May 2009

In a recent paper [1], Jones extended the definition of the convolution of distributions so that further convolutions could be defined. The convolution w1*w2 of two distributions w1 and w2 was defined as the limit ofithe sequence {wln*w2n}, provided the limit w exists in the sense that

for all fine functions ф in the terminology of Jones [2], where

w1n(x) = wl(x)τ(x/n), W2n(x) = w2(x)τ(x/n)

and τ is an infinitely differentiable function satisfying the following conditions:

(i) τ(x) = τ(—x),

(ii)0 ≤ τ (x) ≤ l,

(iii)τ (x) = l for |x| ≤ ½,

(iv) τ (x) = 0 for |x| ≥ 1.
Characterization of certain differential operators in the solution of linear partial differential equations
Authors: Heersink Rudolf
Published: May 2009

In this paper we consider differential equations of the form

where the coefficients Ai are holomorphic functions in a domain G1 × G2 ⊂ C × C. We restrict our attention to those equations for which it is possible to represent the solutions in the form

where g1(z1) and g2(z2) are arbitrary holomorphic functions in G1 and G2 respectively. The coefficients a1, k and a2, k depend on the given differential equation. Within the last ten years a number of publications have been devoted to this kind of representation of solutions.
The α-regular classes of the generalized symmetric group
Authors: Read E. W.
Published: May 2009

The α-regular classes of any finite groupGare important since they are those classes on which the projective characters ofGwith factor set α take non-zero value, and thus a knowledge of the α-regular classes gives the number of irreducible projective representations ofGwith factor set α (see [4]). Here we look at the particular case of the generalized symmetric groupCmwrSl. The analogous problem of constructing the irreducible projective representations ofCmwrSlhas been dealt with in [6] by generalizing Clifford's theory of inducing from normal subgroups, but unfortunately, it is not in general possible to determine the irreducible projective characters (and hence the α-regular classes) by this method.
On Relations among radical properties
Authors: Sands A. D.
Published: May 2009

In this paper we work in the class of associative rings. The fundamental definitions and properties of radicals may be found in Divinsky [1].If α is a radical class of rings we shall denote the class of semi-simple rings by the radical of a ring R we shall denote by α(R).
The Farey density of norm subgroups of global fields (II)
Authors: Cohen S. D. , Odoni R. W. K.
Published: May 2009

In this paper we shall derive for function fields in one variable over finite constant fields results analogous to [1], where algebraic number fields were considered. The ground field P will be the set of all rational functions in a given transcendent X, with coefficients in k = GF(q), q = pr, p a prime; thus P = k(X).
A note on a pair of integral operators involving Whittaker functions
Authors: Habibullah G. M.
Published: May 2009

In recent years various authors have studied integral operators involving confluent hypergeometric functions Mκ,μ and Wκ,μ. Using the method devised by Fox [2], Saxena [5] obtained the inverse of an integral operator with kernel (xt) μ− ½e− ½xtWκ,μ (xt). Singh [6] derived the solution of an integral equation of convolution type with kernel
On the divisibility of r2(n)
Authors: Scourfield E. J.
Published: May 2009

During the past few years, some papers of P. Deligne and J.-P. Serre (see [2], [9], [10] and other references cited there) have included an investigation of certain properties of coefficients of modular forms, and in particular Serre [10] (see also [11]) obtained the divisibility property (1) below. Let

be a modular form of integral weight k ≧ 1 on a congruence subgroup of SL2(Z), and suppose that each cn belongs to the ring RK of integers of an algebraic number field K finite over Q. For c ∈ RK and m ≧ 1 an integer, write c ≡ 0 (mod m) if c ∈ m RK and c ≢ 0 (mod m) otherwise. Then Serre showed that there exists α > 0 such that

as x → ∞, where throughout this note N(n ≦ x: P) denotes the number of positive integers n ≦ x with the property P.
Semi-field-like affine planes
Authors: Kallaher Michael J.
Published: May 2009

Walker [11] describes a new class of translation planes W(q) of order q2, q ≡ 5(mod 6), with kernel GF(q). A plane in this class has several interesting properties, but we shall be only interested in the following ones possessed by its collineation group G: (i) G is transitive on the affine points of W(q), and (ii) G fixes a point the line at infinity of W(q), and is transitive on the other points of l∞ The smallest member of this class, W(5), also satisfies: (iii) for an affine point the subgroup G is transitive on the affine points ≠ of the line Note also that since W(5) is a translation plane, replacing G with G in (ii) we get a fourth property, call it (iv), satisfied by G. (See Lemma 2.)
Commutators and normal operators
Authors: Crabb M. J. , Spain P. G.
Published: May 2009

Let X be a Banach space and L(X) the Banach algebra of bounded linear operators on X. An operator T in L(X) is hermitian if ∥eitT∥ = 1 (t ∈ R), and is normal if T = R + iJ where R and J are commuting normal operators; R and J are then determined uniquely by T, and we may write T* = R–iJ. These definitions extend those for operators on Hilbert spaces. More details may be found in [1].
Derivations in central separable algebras
Authors: Georgantas George T.
Published: May 2009

GivenNa finite separable normal extension of a fieldF, it is well known that the Brauer group Br(N/F) of classes of central simpleF-algebras split byNis isomorphic with Ext(N*,G), the classes of group extensions ofN* by the Galois groupGofNoverF. In the construction of this isomorphism, a key role is played by the Skolem-Noether Theorem which extends automorphisms to inner automorphisms in central simple algebras.
Primitive skew Laurent polynomial rings
Authors: Jordan D. A.
Published: May 2009

In [8] the author studied the question of the primitivity of an Ore extension R[x, δ], where δ is a derivation of the ring R. If a is an automorphism of R then it can be shown that R[x, α] is primitive if the following conditions are satisfied: (i) no power αsS ≥ 1, of α is inner; (ii) the only ideals of R invariant under α are 0 and R. These conditions are also known to be necessary and sufficient for the skew Laurent polynomial ring R[x, x−1, α] to be simple [9]. The object of this paper is to find conditions which are sufficient for R[x, x−1, α] to be primitive. The results obtained are remarkably similar to those of [8]. Two logically independent conditions are each found to be sufficient for the primitivity of R[x, x−1, α]. Of these, one is also shown to be sufficient for R[x, α] to be primitive. Included in the examples illustrating these results are some applications to the theory of primitive group rings. The basic techniques involved are also applied to produce a counterexample to the converse of a theorem of Goldie and Michler [3] on when R[x, x−1, α] is a Jacobson ring.
Groups of complexes of a representable lattice-ordered group
Authors: Byrd R. D. , Lloyd J. T. , Stepp J. W.
Published: May 2009

In 1954 N. Kimura proved that each idempotent in a semigroup is contained in a unique maximal subgroup of the semigroup and that distinct maximal subgroups are disjoint [13] (or see [6, pp. 21–23]). This generalized earlier results of Schwarz [14] and Wallace [15]. These maximal subgroups are important in the study of semigroups. If G is a group, then the collectionS(G) of nonempty complexes ofGis a semigroup and it is natural to inquire what properties ofGare inherited by the maximal subgroups ofS(G). There seems to be very little literature devoted to this subject. In [5, Theorem 2], with certain hypotheses placed on an idempotent, it was shown that ifGis a lattice-ordered group (“1-group”) then a maximal subgroup ofS(G) containing an idempotent satisfying these conditions admits a natural lattice-order. The main result of this note (Theorem 1) is that ifGis a representable1-group andEis a normal idempotent ofS(G) and a dual ideal of the latticeG, then the maximal subgroup ofS(G) containingEadmits a representable lattice-order.
Unique factorization in rings with right ACC1
Authors: Brungs H. H.
Published: May 2009

If R is an integral domain with maximum condition for principal right ideals—right ACC1—every nonzero non-unit in Rhas irreducible factors, but is not necessarily a product of such factors. Using additional basic factors—called infinite primes in [1]—results about unique factorization in principal right ideal domains have been obtained in [1], [2], and [5].
π-domains, overrings, and divisorial ideals
Authors: Anderson D. D.
Published: May 2009

In this paper we study several generalizations of the concept of unique factorization domain. An integral domain is called a π-domainif every principal ideal is a product of prime ideals. Theorem 1 shows that the class of π-domains forms a rather natural subclass of the class of Krull domains. In Section 3 we consider overrings of π-domains. In Section 4 generalized GCD-domains are introduced: these form an interesting class of domains containing all Prüfer domains and all π-domains.
On the Occurrence of large gaps between prime numbers
Authors: Cook R. J.
Published: May 2009

Let pn denote the nth prime number. Erdös asked whether

for some constant c<1. Moreno [7] obtained a somewhat weaker result and subsequently Wolke [10] proved that
Solution to a problem of A. D. Sands
Authors: Fraser Owen H. , Gordon Basil
Published: May 2009

Let G be a finite additive abelian group, and suppose that A and B are subsets of G. We say that G = A⊕B if every element g ∈ G can be uniquely written in the form g = a + b, where a ∈ A, b ∈ B. The study of such decompositions (usually called factorizations in the literature) was initiated by G. Hájos [3] in connection with his solution to a problem of Minkowski in the geometry of numbers.
Convergent processes, projective systems of measures and martingale decompositions
Authors: Blake Louis H.
Published: May 2009

The purpose of this paper is to show the equivalence of convergence, an associated projective system of measures and a martingale decomposition for a uniformly integrable stochastic process. Emphasis is placed on a direct juxtaposition of these concepts and on displaying underlying mechanisms.

The impact of the martingale convergence theorem on contemporary probability theory has been immense. Therein lies the reason for numerous generalizations of both the basic martingale convergence theorem and the martingale concept itself.
Normal operators on Banach spaces
Authors: Fong Che-Kao
Published: May 2009

A (bounded, linear) operator H on a Banach space is said to be hermitian if ∥exp(itH)∥ = 1 for all real t. An operator N on is said to be normal if N = H + iK, where H and K are commuting hermitian operators. These definitions generalize those familiar concepts of operators on Hilbert spaces. Also, the normal derivations defined in [1] are normal operators. For more details about hermitian operators and normal operators on general Banach spaces, see [4]. The main result concerning normal operators in the present paper is the following theorem.
Non-secular, locally compact TRL groups
Authors: Redfield R. H.
Published: May 2009

In [12], Loy and Miller proved that a locally compact, eudoxian TR group is algebraically and order-theoretically (and hence, topologically) isomorphic to a finite product of copies of the real numbers. In [18], Wirth used their result to describe the subgroup of a locally compact TR group generated by the compact neighbourhoods of zero. The proof of Loy and Miller relied heavily on a result of Mackey (cf. [10], p. 390) and either the finite-dimensional case of the Choquet-Kendall Theorem (cf. [15], pp. 9–10) or the representation theory of Kakutani (cf. [11], Appendix). Below we use only elementary topological results and order-theoretic arguments and a theorem of Conrad [4] to characterize all non-secular, locally compact TRL groups (Theorem 3). Our proof of Theorem 3 allows us to deduce algebraically the theorems both of Loy and Miller and of Wirth, in both cases without appealing to the theorem of Conrad.
Completions of semilattices of cancellative semigroups
Authors: Burgess W. D.
Published: May 2009

A semilattice of cancellative semigroupsSis a p.o. semigroup with the order relationa≤biffab=a2. IfSis a strong semilattice of cancellative semigroups (i.e., multiplication inSis given by structure maps ϕe,f(f≤einE)), for each supremum-preserving completion Ē of the semilatticeEthere is a strong semilattice of cancellative semigroupsTover Ē which is a supremum-preserving completion ofSin ≤. Given Ē,Tis constructed directly. In this paper it is shown that multiplication by an element ofSdistributes over suprema in ≤ ifEhas this property (called strong distributivity). Next it is shown that the completion construction also applies to a semilattice of cancellative semigroups which is not strong ifSis commutative and Ē is strongly distributive. Finally, it is shown that for semilattices of cancellative monoids a completion is completely determined, up to isomorphism overS, by completions ofE.
Order-Topological lattices
Authors: Erné Marcel
Published: May 2009

The observation that convergence of real sequences may be defined in terms of limits inferior and limits superior as by means of neighbourhoods in the Euclidean topology leads to the question: for which lattices does order convergence coincide with convergence in the order topology? This problem has been attacked by D. C. Kent [10], A. Gingras [7] and others. We hope to present a satisfactory solution in this paper. Although there are known several characterizations of lattices, with topological order convergence (cf. Propositions 1, 2), an evaluation of these criteria already requires some knowledge of the order topology of the given lattice. In the present paper, we establish a purely lattice-theoretical description of those lattices for which order convergence is not only topological, but moreover, the lattice operations are continuous. Henceforth, such lattices will be referred to as order-topological lattices. All convergence statements will be formulated in terms of filters rather than nets. For an introduction to convergence functions, the reader may consult D. C. Kents's paper [9].
Bifurcation from Eigenvalues in Non-Linear Multiparameter Sturm-Liouville Problems
Authors: Browne Patrick J. , Sleeman B. D.
Published: May 2009

This paper continues our study of non-linear multiparameter eigenvalue problems. In recent work [3], [4], [5] we have discussed bifurcation from eigenvalues in both abstract and concrete multiparameter problems. In this note we present further simple conditions which will ensure bifurcation from eigenvalues of a multiparameter Sturm-Liouville problem. We consider the regular case and the asymptotic case of bifurcation from infinity.
Compact actions on C*-algebras
Authors: Akemann Charles A. , Wright Steve
Published: May 2009

In Section 33 of [2], Bonsall and Duncan define an elementtof a Banach algebratoact compactlyonif the mapa→tatis a compact operator on. In this paper, the arguments and technique of [1] are used to study this question for C*-algebras (see also [10]). We determine the elementsbof a C*-algebrafor which the mapsa→ba,a→ab,a→ab+ba,a→babare compact (respectively weakly compact), determine the C*-algebras which are compact in the sense of Definition 9, of [2, p. 177] and give a characterization of the *-automorphisms ofwhich are weakly compact perturbations of the identity.
Localization in non-noetherian group rings
Authors: Smith P. F.
Published: May 2009

Let k be a field and G an Abelian group of finite torsion-free rank. Brewer, Costa and Lady [1, Theorem A] showed that if k has characteristic 0 then each Localization of the group algebra kG at a prime ideal is a regular local ring. They also showed (in the same theorem) that if k has characteristic p>0, then kG is locally Joetherian (i.e. each localization of kG at a prime ideal is a Noetherian ring) if and only if G is an extension of a finitely generated group by a torsion p′-group. The purpose of this note is to examine this theorem in a more general setting.
A common generalization of local cohomology theories
Authors: Bijan-Zadeh M. H.
Published: May 2009

Throughout this note all rings considered will be commutative and noetherian and will have non-zero identity elements. A will always denote such a ring and the category of all A-modules and all A-homomorphisms will be denoted by A.
Solution of Irving's Ramsey problem
Authors: Harborth Heiko , Nitzschke Heinz-Michael
Published: May 2009

In [1] the following question was posed by R. W. Irving (see also Conjecture 4.10 in [4]): Is there an edge 2-colouring of the complete bipartite graph K13,17 with no monochromatic K3,3? We give a negative answer in this note (Theorem 2). Furthermore we prove Conjecture 4.11 (i) of [4] (Theorem 1), that is, any edge 2-coloured K2n+1,4n−3 contains a monochromatic K2,n with the 2 and n vertices a subset of the 2n+1 and 4n−3 vertices, respectively. Theorem 1 is a consequence of Satz 4 in [3], however, we give a direct proof here.
The group of isometries on Hardy spaces of the n-ball and the polydisc
Authors: Berkson Earl , Porta Horacio
Published: May 2009

Let C be the complex plane, and U the disc |z| < 1 in C. Cn denotes complex n-dimensional Euclidean space, <, > the inner product, and | · | the Euclidean norm in Cn. Bn will be the open unit ball {z ∈ Cn: |z| < 1}, and Un will be the unit polydisc in Cn. For 1 ≤p<∞, p≠2, Gp(Bn) (resp., Gp (Un)) will denote the group of all isometries of Hp (Bn) (resp., Hp (Un)) onto itself, where Hp (Bn) and Hp (Un) are the usual Hardy spaces.
Autoclinisms and automorphisms of finite groups II
Authors: Tappe Jürgen
Published: May 2009

In part I of this paper P. Hall's formula for finite stem groups was derived. Using results of C. R. Leedham-Green and S. McKay, a similar formula for isoclinic groups with arbitrary branch factor group is shown.
Weight functions on extensions of the compound manual
Authors: Frazer Patricia J. , Foulis David J. , Randall Charles H.
Published: May 2009

It has been shown ([8], [2], [1], [3], [9]) that a collection of physical operations or experiments can be represented by a nonempty set of nonempty sets satisfying certain technical conditions. Such a set is called a manual. The operations in are looked at as having no “before” and no “after”, i.e., they are isolated in time. If we wish to look at connected sequences of operations—in particular, if we wish to condition by events in —we must look at the compound manual c whose elements represent compound operations built up from the operations in the base manual .
Results on common fixed points on complete metric spaces
Authors: Fisher Brian
Published: May 2009

The following theorem was proved in [1].

Theorem 1. Let S and T be continuous, commuting mappings of a complete, bounded metric space (X, d) into itself satisfying the inequality

for all x, y in X, where 0 ≤ c < 1 and p, p′, q, q′ ≥ 0 are fixed integers with p + p′, q + q′ ≥ 1. Then S and T have a unique common fixed point z. Further, if p′ or q′ = 0, then z is the unique fixed point of S and if p or q = 0, then z is the unique fixed point of T.
Autoclinisms and automorphisms of finite groups II
Authors: Tappe Jürgen
Published: May 2009

In part I of this paper P. Hall's formula for finite stem groups was derived. Using results of C. R. Leedham-Green and S. McKay, a similar formula for isoclinic groups with arbitrary branch factor group is shown.

The main result of this paper is the following theorem, which appears without proof in [1, p. 203].
On the kernels of representations of finite groups
Authors: Koshitani Shigeo
Published: May 2009

Let G be a finite group and p a prime number. About five years ago I. M. Isaacs and S. D. Smith [5] gave several character-theoretic characterizations of finite p-solvable groups with p-length 1. Indeed, they proved that if P is a Sylow p-subgroup of G then the next four conditions (l)–(4) are equivalent:

(1) G is p-solvable of p-length 1.

(2) Every irreducible complex representation in the principal p-block of G restricts irreducibly to NG(P).

(3) Every irreducible complex representation of degree prime to p in the principal p-block of G restricts irreducibly to NG(P).

(4) Every irreducible modular representation in the principal p-block of G restricts irreducibly to NG(P).
Integral ∨-ideals
Authors: Anderson David F.
Published: May 2009

Let R be an integral domain with quotient field K. A fractional ideal I of R is a ∨-ideal if I is the intersection of all the principal fractional ideals of R which contain I. If I is an integral ∨-ideal, at first one is tempted to think that I is actually just the intersection of the principal integral ideals which contain I.However, this is not true. For example, if R is a Dedekind domain, then all integral ideals are ∨-ideals. Thus a maximal ideal of R is an intersection of principal integral ideals if and only if it is actually principal. Hence, if R is a Dedekind domain, each integral ∨-ideal is an intersection of principal integral ideals precisely when R is a PID.
Chapter 2 of Ramanujan's second notebook
Authors: Berndt Bruce C. , Joshi Padmini T. , Wilson B. M.
Published: May 2009

When Ramanujan died in 1920 he left behind three notebooks containing statements of a few thousand theorems, mostly without proofs. The second notebook is an enlarged edition of the first, and the third is short and fragmentary. Thus our primary attention may be directed toward the second notebook. In the decade following Ramanujan's death, G. N. Watson and B. M. Wilson agreed to perform the enormous task of editing the notebooks. Unfortunately, this task was never completed, possibly, in part, due to the premature death of Wilson in 1935. In 1957, a photostat edition [19] of the notebooks was published, but no editing whatsoever was undertaken.
Fixed points and their approximation in Banach spaces for certain commuting mappings
Authors: Khan M. S.
Published: May 2009

1. Let X be a Banach space. Then a self-mapping A of X is said to be nonexpansive provided that ‖AX − Ay‖≤‖X − y‖ holds for all x, y ∈ X. The class of nonexpansive mappings includes contraction mappings and is properly contained in the class of all continuous mappings. Keeping in view the fixed point theorems known for contraction mappings (e.g. Banach Contraction Principle) and also for continuous mappings (e.g. those of Brouwer, Schauderand Tychonoff), it seems desirable to obtain fixed point theorems for nonexpansive mappings defined on subsets with conditions weaker than compactness and convexity. Hypotheses of compactness was relaxed byBrowder [2] and Kirk [9] whereas Dotson [3] was able to relax both convexity and compactness by using the notion of so-called star-shaped subsets of a Banach space. On the other hand, Goebel and Zlotkiewicz [5] observed that the same result of Browder [2] canbe extended to mappings with nonexpansive iterates. In [6], Goebel-Kirk-Shimi obtainedfixed point theorems for a new class of mappings which is much wider than those of nonexpansive mappings, and mappings studied by Kannan [8]. More recently, Shimi [12] used the fixed point theorem of Goebel-Kirk-Shimi [6] to discuss results for approximating fixed points in Banach spaces.
Some examples of modules over Noetherian rings
Authors: Musson I. M.
Published: May 2009

The purpose of this note is to prove the following result.

Theorem 1.Let n be an integer greater than zero. There exists a prime Noetherian ring R of Krull dimension n + 1 and a finitely generated essential extension W of a simple R-module V suchthat

(i)W has Krull dimension n, and

(ii)W/V is n-critical and cannot be embedded in any of its proper submodules.

We refer the reader to [6] for the definition and properties of Krull dimension.
Uniform distribution of sequences in rings of integral quaternions
Authors: Kuipers L. , Shiue Jau-Shyong
Published: May 2009

Let ℤ and ℤ[i] have their usual meaning. Let Yo denote the noncommutative ring of integral quaternions, that is the set of all elements a + bi + cj + dk with a, b, c, d ∈ ℤ and where i, j and k together with the number 1 are the four units of the system of quaternions.
Some topological properties of residually Černikov groups
Authors: Dixon M. R.
Published: May 2009

In this paper we shall indicate how to generalise the concept of a cofinite group (see [7]). We recall that any residually finite group can be made into a topological group by taking as a basis of neighbourhoods of the identity precisely the normal subgroups of finite index. The class of compact cofinite groups is then easily seen to be the class of profinite groups, where a group is profinite if and only if it is an inverse limit of finite groups. It turns out that every cofinite group can be embedded as a dense subgroup of a profinite group. This has important consequences for the class of countable locally finite-soluble groups with finite Sylow p-subgroups for all primes p, as shown in [7] and [14].
Lifting sets and the Calkin algebra
Authors: Murphy G. J.
Published: May 2009

H will denote a Hilbert space of infinite dimension, ℬ(H) the algebra of bounded linear operators on H, and ℛ(H) the ideal of compact operators on H. We let σ, σe and σω denote the spectrum, essential spectrum and Weyl spectrum respectively. It is well known that for arbitrary T ∈ ℬ(H) we have by [5]

and

and
A characterization of normed M-spaces
Authors: Schmidt Garfield C.
Published: May 2009

Linear spaces on which both an order and a topology are defined and related in various ways have been studied for some time now. Given an order on a linear space it is sometimes possible to define a useful topology using the order and linear structure. In this note we focus on a special type of space called a linear lattice and determine those lattice properties which are both necessary and sufficient for the existence of a classical norm, called an M-norm, for the lattice. This result is a small step in a program to determine which intrinsic order properties of an ordered linear space are necessary and sufficient for the existence of various given types of topologies for the space. This study parallels, in a certain sense, the study of purely topological spaces to determine intrinsic properties of a topology which make it metrizable and the study of the relation between order and topology on spaces which have no algebraic structure, or. algebraic structures other than a linear one.
A class of maximal orders integral over their centres
Authors: Gray Andy J.
Published: May 2009

In a recent paper [1], Brown, Hajarnavis and MacEacharn have considered non-commutative Noetherian local rings of finite global dimension which are integral over their centres. For such a ring Rthey have shown:

(i) R is a prime ring whose Krull and global dimensions coincide;

(ii) R = ∩ RP where p runs through the set of rank one primes of the centre of R, and each Rp is hereditary;

(iii) the centre of R is a Krull domain.
On an integral equation of Šub-Sizonenko
Authors: Rooney P. G.
Published: May 2009

The integral equation of the title is

It was studied in [4], though h(x) was written as x-1g(x-1) there, and using a method involving orthogonal Watson transformations, it was shown there that if h ∈ L2(0, ∞), then the equation has a solution f ∈ L2(0, ∞), and that / is given by

In this paper, using the techniques of [3], we shall show that the equation can be solved for ℎ in the space ℒμ, p of [3] for 1 ≤ p < ∘, μ > 0, and that for these spaces, which include L2(0, ∘), f is given by the simpler formula

We shall further show that these results can be extended to the spaces ℒw, μ, p of [3]. This forms the content of our theorem below.
Addendum to a paper of M. Saks
Authors: Perfect Hazel
Published: May 2009

Throughout, (X, ≤ ) denotes a partially ordered set (p. o. set), where X is assumed to be finite. A subset Y of X is called a k-union if Y contains no chain of length K + 1. In particular, therefore, a 1-union is just an antichain; and it is readily seen that Y is a k-union if and only if it is a union of K antichains. (Dually, a subset Z of X is a k-counion if Z contains no antichain of length k + 1.) We denote by dk (X) the maximum cardinality of a k-union in X, with a similar notation for other p. o. sets. Now let be any partition of X into chains, and write

.
A base norm space whose cone is not 1-generating
Authors: Yost David
Published: May 2009

Let E be an ordered Banach space with closed positive cone C. A base for C is a convex subset K of C with the property that every non-zero element of C has a unique representation of the form λk with λ > 0 and k ∈ K. Let S be the absolutely convex hull of K. If the Minkowski functional of S coincides with the given norm on E, then E is called a base norm space. Then K is a closed face of the unit ball of E, and S contains the open unit ball of E. Base norm spaces were first defined by Ellis [5, p. 731], although the special case of dual Banach spaces had been studied earlier by Edwards [4].
A bounded map associated to a one-parameter group of *-automorphisms of a von Neumann algebra
Authors: Thaheem A. B.
Published: May 2009

Let M be a von Neumann algebra and a strongly continuous one-parameter group of *-automorphisms of M. Recently, considerable interest has been shown in the associated mappings (see for instance [2], [3] and [4]). The paper of Thaheem, Van Daele and Vanheeswijk [4] exclusively deals with these mappings. The main result of [4] is formulated as follows. Let and be strongly continuous one-parameter groups of *-automorphisms on a von Neumann algebra M satisfying the operator equation
Embedding any countable semigroup in a 2-generated bisimple monoid
Authors: Byleen Karl
Published: May 2009

G. B. Preston [10] proved that any semigroup can be embedded in a bisimple monoid. If S is a countable semigroup, his constructive proof yields a bisimple monoid which is also countable, but not necessarily finitely generated. The main result of this paper is that any countable semigroup can be embedded in a 2-generated bisimple monoid.

J. M. Howie [6] proved that any semigroup can be embedded in an idempotentgenerated semigroup. F. Pastijn [9] showed that any semigroup can be embedded in a bisimple idempotent-generated semigroup, and that any countable semigroup can be embedded in a semigroup which is generated by 3 idempotents. Easy proofs of these results using Rees matrix semigroups over a semigroup were given by the author [3]. In this paper, as a corollary to our main result, we deduce that any countable semigroup can be embedded in a bisimple semigroup which is generated by 3 idempotents.
Generation of the lower central series II
Authors: Guralnick Robert M.
Published: May 2009

In this article, we obtain results on commutators in Sylow subgroups of the lower central series, extending the work of Dark and Newell [2], Rodney [12, 13] and Aschbacher and the author [1, 6, 7].

Some notation is required for the statement of the main results. Let r be a positive integer and define

and

where x1, …, xr, are elements in a group G. Let ΓrG = {[x1, …, xr]∣ x1 ∈ G} be the set of r-fold commutators in G. Then Lr,G = 〈ΓrG〉 is the rth term in the lower central series of G. Set L∞G = ∩ Lr,G.
Rings all of whose torsion quasi-injective modules are injective
Authors: Ahsan J. , Enochs E.
Published: May 2009

Throughout this paper it is assumed that rings are associative, have the identity element, and all modules are left unital. R will denote a ring with identity, R-Mod the category of left R-modules, and for each left R-module M, E(M) (resp. J(M)) will represent the injective hull (resp. Jacobson radical) of M. Also, for a module M, A ⊆' M will mean that A is an essential submodule of M, and Z(M) denotes the singular submodule of M. M is called singular if Z(M) = M, and it is called non-singular in case Z(M) = 0. For fundamental definitions and results related to torsion theories, we refer to [12] and [14]. In this paper we shall deal mainly with Goldie torsion theory. Recall that a pair (G, F) of classes of left R-modules is known as Goldie torsion theory if G is the smallest torsion class containing all modules B/A, where A ⊆' B, and the torsion free class F is precisely the class of non-singular modules.
Free completely regular semigroups
Authors: Trotter P. G.
Published: May 2009

A completely regular semigroup is a semigroup that is a union of groups. The aim here is to provide an alternative characterization of the free completely regular semigroup Fcrx on a set X to that given by J. A. Gerhard in [3, 4].

Although the structure theory for completely regular semigroups was initiated in 1941 [1] by A. H. Clifford it was not until 1968 that it was shown by D. B. McAlister [5] that Fcrx exists. More recently, in [7], M. Petrich demonstrated the existence of Fcrx by showing that completely regular semigroups form a variety of unary semigroups (that is, semigroups with the additional operation of inversion).
A note on Clifford algebras and central division algebras with involution
Authors: Lewis D. W.
Published: May 2009

In this note we consider the question as to which central division algebras occur as the Clifford algebra of a quadratic form over a field. Non-commutative ones other than quaternion division algebras can occur and it is also the case that there are certain central division algebras D which, while not themselves occurring as a Clifford algebra, are such that some matrix ring over D does occur as a Clifford algebra. We also consider the further question as to which involutions on the division algebra can occur as one of two natural involutions on the Clifford algebra.
Multiplier systems for Hilbert's and Siegel's modular groups
Authors: Gundlach Karl-Bernhard
Published: May 2009

The classical generalizations (already investigated in the second half of last century) of the modular group SL(2, ℤ) are the groups ГK= SL(2,o)(othe principal order of a totally real number fieldK, [K:ℚ]=n), operating, originally, on a productofnupper half-planes or, forn=2, on the product1×−of an upper and a lower half-plane by

(wherev(i), forv∈K, denotes the jth conjugate ofv), and Гn= Sp(n, ℤ), operating onn={Z∣Z=X+iY∈ℂ(n,n),tZ=Z, Y>0} by

Nowadays ГKis called Hilbert's modular group ofKand ГnSiegel's modular group of degree (or genus)n.Forn=1 we have Гℚ=Г1= SL(2, ℤ). The functions corresponding to modular forms and modular functions for SL(2, ℤ) and its subgroups are holomorphic (or meromorphic) functions with an invariance property of the form

J(L, t)for fixedL(orJ(M, Z)for fixedM) denoting a holomorphic function without zeros on) (or onn). A functionJ;, defined on ℤK×or ℤn×nto be able to appear in (1.3) withf≢0, has to satisfy certain functional equations (see below, (2.3)–(2.5) for ГK, (5.7)–(5.9) for Гn) and is called an automorphic factor (AF) then. In close analogy to the casen=1, mainly AFs of the following kind have been used:

with a complex numberr, the weight ofJ, and complex numbersv(L), v(M). AFs of this kind are called classical automorphic factors (CAP) in the sequel. Ifr∉ℤ, the values of the functionvon ГK(or Гn) depend on the branch of (…)r. For a fixed choice of the branch (for eachL∈ГKorM∈Гn) the functional equations forJ, by (1.4), (1.5), correspond to functional equations forv.A functionvsatisfying those equations is called a multiplier system (MS) of weightrfor ГK(or Гn).
Small solutions of quadratic congruences
Authors: Heath-Brown D. R.
Published: May 2009

Let Q(x) = Q(x1, …, xn)∈ℤ[x1, …, xn] be a quadratic form. We investigate the size of the smallest non-zero solution of the congruence Q(x)≡0 (mod q). We seek a bound Bn(q), independent of Q, such that there is always a non-zero solution satisfying

The form gives the trivial lower bound Bn(q)≥(q/n)½ for all q and n, since if x≠0 and q∣ Q(x), then Q(x)≥q.
on l-adic representations attached to modular forms II
Authors: Ribet Kenneth A.
Published: May 2009

Suppose that is a newform of weight k on Г1(N). Thus f is in particular a cusp form on Г1(N), satisfying

for all n≥1. Associated with f is a Dirichlet character

such that

for all, .
Compactifications of totally bounded quasi-uniform spaces
Authors: Fletcher P. , Lindgren W. F.
Published: May 2009

The notation and terminology of this paper coincide with that of reference [4], except that here the term, compactification, refers to a T1-space. It is known that a completely regular totally bounded Hausdorff quasi-uniform space (X, ) has a Hausdorff compactification if and only if contains a uniformity compatible with ℱ() [4, Theorem 3.47]. The use of regular filters by E. M. Alfsen and J. E. Fenstad [1] and O. Njåstad [5], suggests a construction of a compactification, which differs markedly from the construction obtained in [4]. We use this construction to show that a totally bounded T1 quasi-uniform space has a compactification if and only if it is point symmetric. While it is pleasant to have a characterization that obtains for all T1-spaces, the present construction has several further attributes. Unlike the compactification obtained in [4], the compactification given here preserves both total boundedness and uniform weight, and coincides with the uniform completion when the quasi-uniformity under consideration is a uniformity. Moreover, any quasi-uniformly continuous map from the underlying quasi-uniform space of the compactification onto any totally bounded compact T1-space has a quasi-uniformly continuous extension to the compactification. If is the Pervin quasi-uniformity of a T1-space X, the compactification we obtain is the Wallman compactification of (X, ℱ ()). It follows that our construction need not provide a Hausdorff compactification, even when such a compactification exists; but we obtain a sufficient condition in order that our compactification be a Hausdorff space and note that this condition is satisfied by all uniform spaces and all normal equinormal quasi-uniform spaces. Finally, we note that our construction is reminiscent of the completion obtained by Á. Császár for an arbitrary quasi-uniform space [2, Section 3]; in particular our Theorem 3.7 is comparable with the result of [2, Theorem 3.5].
Joint spectra of operators on Banach space
Authors: Chō Muneo
Published: May 2009

Let X be a complex Banach space. We denote by B(X) the algebra of all bounded linear operators on X. Let = (T1, …, Tn) be a commuting n-tuple of operators on X. And let στ() and σ″() by Taylor's joint spectrum and the doubly commutant spectrum of , respectively. We refer the reader to Taylor [8] for the definition of στ() and σ″(), A point z = (z1,…, zn) of ℂn is in the joint approximate point spectrum σπ() of if there exists a sequence {xk} of unit vectors in X such that

∥(Ti – zi)xk∥→0 as k → ∞ for i = 1, 2,…, n.
Class groups and automorphism groups of group rings
Authors: Brown Kenneth A.
Published: May 2009

This paper is a sequel to [2]. A polycyclic-by-finite group G was there called dihedral free if G contains no subgroup isomorphic to 〈b, a:ba = b-1 a2 = 1〉 whose normalizer has finite index in G. It was shown in [2, Theorem F] that, if R is a commutative Noetherian domain, the group ring RG is a prime Noetherian maximal order if and only if R is integrally closed, G is dihedral free, and G has no non-trivial finite normal subgroups. Throughout, R and G will be assumed to satisfy these hypotheses. The main aim of the paper is to study the class group of the maximal order RG.
Groups whose automorphisms are almost determined by their restriction to a subgroup
Authors: Pettet Martin R.
Published: May 2009

The trivial observation that every automorphism of a group is determined by its restriction to a set of generators suggests the converse question: if X is a subset of a group G such that each automorphism of G is determined (or “almost” determined) by its restriction to X, to what extent is the structure of G governed by that of the subgroup which X generates? Is this subgroup in some sense necessarily “large” in G? If the index of the subgroup is used as a measure of largeness, then in the absence of additional hypotheses, the answer to the second question is generally “no”, the additive group of rationals with X = {1} being an obvious counterexample. (More confounding is the existence of uncountable torsion-free abelian groups for which inversion is the only non-trivial automorphism. See, for example, [2], [3], and [4].) However, under certain finiteness assumptions, it seems that some positive conclusions are obtainable. One such example will be considered here.
On normally embedded subgroups of locally soluble FC-groups
Authors: Beidleman J. C. , Karbe M. J.
Published: May 2009

In his Habilitationsschrift [3] B. Fischer introduced the concept of a normally embedded subgroup of a finite group. A subgroup of a finite group G is said to be normally embedded in G if each of its Sylow subgroups is a Sylow subgroup of a normal subgroup of G. Meanwhile this concept has become of considerable importance in the theory of finite soluble groups and has been studied by various authors. However, in infinite group theory, normally embedded subgroups seem to have received little attention. The object of this note is to study normally embedded subgroups of locally soluble FC-groups.
Free bands and free *-bands
Authors: Gerhard J. A. , Petrich Mario
Published: May 2009

The word problem for free bands (idempotent semigroups) was solved by Green and Rees [4] in an early paper. They also established certain properties of the free band. This was followed by McLean [6] who provided a general structure theory for bands with some indication as to the structure of the free band. Since then a great many papers have appeared dealing with various aspects of the topic of bands and their varieties. A different solution of the word problem for free bands was recently given by Siekmann and Szabó [9]. For a discussion of bands, see the books [5] and [8].
Approximate point spectrum and commuting compact perturbations
Authors: Rakočević Vladimir
Published: May 2009

Let X be an infinite-dimensional complex Banach space and denote the set of bounded (compact) linear operators on X by B (X) (K(X)). Let σ(A) and σa(A) denote, respectively, the spectrum and approximate point spectrum of an element A of B(X). Set

σem(A)and σeb(A) are respectively Schechter's and Browder's essential spectrum of A ([16], [9]). σea (A) is a non-empty compact subset of the set of complex numbers ℂ and it is called the essential approximate point spectrum of A ([13], [14]). In this note we characterize σab(A) and show that if f is a function analytic in a neighborhood of σ(A), then σab(f(A)) = f(σab(A)). The relation between σa(A) and σeb(A), that is exhibited in this paper, resembles the relation between the σ(A) and the σeb(A), and it is reasonable to call σab(A) Browder's essential approximate point spectrum of A.
Factorization and bounded approximate identities for a class of convolution Banach algebras
Authors: Ouzomgi S. I.
Published: May 2009

An algebra A factors if, for each a ∈ A, there exist b, c ∈ A with a = bc. A bounded approximate identity for a Banach algebra A is a net (eα) ⊂ A such that aeα → a and eαa → a for each a ∈ A and such that sup ‖eα ‖ < ∞. It is well known [2, 11.10] that if A has a bounded approximate identity, then A factors. But a Banach algebra may factor even if it does not have a bounded approximate identity: an example which is non-commutative and separable, and an example which is commutative and nonseparable, are given in [3, §22]. However, we do not know an example of a commutative, separable Banach algebra which factors, but which does not have a bounded approximate identity. See 4 for related work.
Non-abelian exterior products of groups and exact sequences in the homology of groups
Authors: Ellis G. J.
Published: May 2009

Various authors have obtained an eight term exact sequence in homology

from a short exact sequence of groups

,

the term V varying from author to author (see [7] and [2]; see also [5] for the simpler case where N is central in G, and [6] for the case where N is central and N ⊂ [G, G]). The most satisfying version of the sequence is obtained by Brown and Loday [2] (full details of [2] are in [3]) as a corollary to their van Kampen type theorem for squares of spaces: they give the term V as the kernel of a map G ∧ N → N from a “non-abelian exterior product” of G and N to the group N (the definition of G ∧ N, first published in [2], is recalled below). The two short exact sequences

and

where F is free, together with the fact that H2(F) = 0 and H3(F) = 0, imply isomorphisms

.

.

The isomorphism (2) is essentially the description of H2(G) proved algebraically in [11]. As noted in [2], the isomorphism (3) is the analogue for H3(G) of the Hopf formula for H2(G).
Generic isotopies of space curves
Authors: Bruce J. W. , Giblin P. J.
Published: May 2009

For a single space curve (that is, a smooth curve embedded in ℝ3) much geometrical information is contained in the dual and the focal set of the curve. These are both (singular) surfaces in ℝ3, the dual being a model of the set of all tangent planes to the curve, and the focal set being the locus of centres of spheres having at least 3-point contact with the curve. The local structures of the dual and the focal set are (for a generic curve) determined by viewing them as (respectively) the discriminant of a family derived from the height functions on the curve, and the bifurcation set of the family of distance-squared functions on the curve. For details of this see for example [6, pp. 123–8].
Generalisation de la decomposition de kato aux opérateurs paranormaux et spectraux
Authors: Mbekhta Mostafa
Published: May 2009

Dans tout ce qui suit,Hdésigne un espace de Hilbert séparable,Aun opérateur fermé de domaineD(A) dansH, on noteB(H) l'ensemble des opérateurs bornés deHdans lui-même etN(A),R(A) respectivement le noyau deA, l'image deA.

En 1958, T. Kato a démontré dans [7] le théorème suivant.
The spectrum of orthogonal sums of subnormal pairs
Authors: Rudol K.
Published: May 2009

This note provides yet another example of the difficulties that arise when one wants to extend the spectral theory of subnormal operators to subnormal tuples. Several basic properties of a subnormal operator Y remain true for tuples; e.g. the existence and uniqueness of its minimal normal extension N, the spectral inclusion σ(N)⊂ σ(Y)-proved for n-tuples in [4] and generalized to infinite tuples in [5]. However, neither the invariant subspace theorem nor the spectral mapping theorem in the “strong form” as in [3] is known so far for subnormal tuples.