Generalization of a problem of Evelyn-Linfoot and Page in additive number theory

Summary Let k and l be integers such that 2k l. Let S_k and S _{l l}be two subsets of positive integers with S_kQ_k and S_l Q_l, where Q_k denotes the set of k-free integers. Further suppose that the characteristic functions of S_k and S _{l l} are multiplicative. Let T(n) denote the number of representations of n in the form n=a+b, where a S_k and b S _{l l}. In this paper we establish an asymptotic formula for T(n), when n is sufficiently large; and deduce several known asymptotic formulae as particular cases.     

A remark on almost complete intersections

Let k be a perfect field and S the quotient ring of a polynomial ring k[X₁,...,X_t] with respect to a prime ideal. Let I be a prime ideal of S such that R=S/I is an almost complete intersection. Then, in his paper [2], Matsuoka proves that the homological dimension of the differential module _R/Kis infinite under the assumption that R is Cohen-Macaulay and I² is a primary idea]. In this paper we prove that the result is valid without the above assumption.     

On almost complete intersections

Let R be a local ring such that R=S/I where S is a regular local ring and I is a prime ideal of height r. In this paper it is shown that if I is minimally generated by r+1 elements, then there exists an R-homomorphism : K_RR^r+1 such that is an injection and R^r+1/(K_R)I/I² where K_R:=Ext _S ^r (R,S) the canonical module of R. Moreover, in case where S is a locality over a perfect field k, it is also shown that if R is Cohen-Macaulay and I² is a primary ideal, then the homological dimension of the differential module _R/k is infinite.The author wishes to thank his colleague Mr.Y.Aoyama for valuable discussions in connection with this subject.     

On the Number of Group-Weighted Matchings

Let G be a bipartite graph with a bicoloration {A,B}, |A|=|B|. Let E(G) A x B denote the edge set of G, and let m(G) denote the number of perfect matchings of G. Let K be a (multiplicative) finite abelsian group |K| = k, and let w:E(G) K be a weight assignment on the edges of G. FOr S E(G) let w(S) = _eSw(e). A perfect matching M of G is a w-matching if w(M)=1. We shall be interested in m(G,w), the number of w-matchings of G.It is shown that if deg(a) d for all a A, then either G has no w-matchings, or G has at least (d - k + 1)! w-matchings.     

Decidability of complexity one-half for finite semigroups

Resume All semigroups considered are finite. The semigroup C is by definition combinatorial (or group free or aperiodic) iff the maximal subgroups of C are singletons. Let S₂oS₁ denote the wreath product of S₁ by S₂, so P₁: S₂oS₁ → S₁ with P₁ the projection surmorphism. S<T, read S divides T, iff S is a homomorphic image of a subsemigroup of T. In this paper we give necessary and sufficient conditions in terms of a homomorphic image of S (resp. a subsemigroup of S) so that S<GoC (resp. S<CoG), with C a combinatorial semigroup and G a group. This requires an earlier results by Bret Tilson and John Rhodes in [8]. This research was partially supported by a grant from the National Science Foundation.     

Finite orbits for rational functions

Let K be a number field and φ ∈ K(z) a rational function. Let S be the set of all archimedean places of K and all non-archimedean places associated to the prime ideals of bad reduction for φ. We prove an upper bound for the length of finite orbits for φ in ?₁ (K) depending only on the cardinality of S.     

Prime Ideals in Algebras Determined by Submonoids of Nilpotent Groups

The prime spectrum of the semigroup algebra K[S] of a submonoid S of a finitely generated nilpotent group is studied via the spectra of the monoid S and of the group algebra K[G] of the group G of fractions of S. It is shown that the classical Krull dimension of K[S] is equal to the Hirsch length of the group G provided that G is nilpotent of class two. This uses the fact that prime ideals of S are completely prime. An infinite family of prime ideals of a submonoid of a free nilpotent group of class three with two generators which are not completely prime is constructed. They lead to prime ideals of the corresponding algebra. Prime ideals of the monoid of all upper triangular n × n matrices with non-negative integer entries are described and it follows that they are completely prime and finite in number.     

A Remark on Chen’s Theorem (II)

Let p denote a prime and P2 denote an almost prime with at most two prime factors. The author proves that for sufficiently large x,∑p≤x p＋2=P2 1〉1.13Cx/log^2x,where the constant 1.13 constitutes an improvement of the previous result 1.104 due to J. Wu.     

Borel-plus-powers monomial ideals

Let S=K[x₁,…,x_n] be a standard graded polynomial ring over a field K. In this paper, we show that the lex-plus-powers ideal has the largest graded Betti numbers among all Borel-plus-powers monomial ideals with the same Hilbert function. In addition in the case of characteristic 0, by using this result, we prove the lex-plus-powers conjecture for graded ideals containing , where p is a prime number.     

Gelfand Factor Rings and Weak Zariski Topologies

Let R be any ring with identity. Let N(R) (resp. J(R)) denote the prime radical (resp. Jacobson radical) of R, and let Spec _r (R) (resp. Spec _l (R), Max _r (R), Prim _r (R)) denote the set of all right prime ideals (resp. all left prime ideals, all maximal right ideals, all right primitive ideals) of R. In this article, we study the relationships among various ring-theoretic properties and topological conditions on Spec _r (R) (with weak Zariski topology). The following results are obtained: (1) R/N(R) is a Gelfand ring if and only if Spec _r (R) is a normal space if and only if Spec _l (R) is a normal space; (2) R/J(R) is a Gelfand ring if and only if every right prime ideal containing J(R) is contained in a unique maximal right ideal.     

Primary Ideals and Valuation Ideals in Semigroups

Let S be a cancellation torsion-free additive semigroup with identity 0 and let S {0}. We consider the relation between the valuation ideals and primary ideals of S. We give a characterization that each primary ideal is a valuation ideal in S and also give a characterization that each valuation ideal is a primary ideal in S.AMS Subject Classification (1991): 20M14     

Ascending chain conditions on principal left and right ideals for semidirect products of semigroups

In this paper we investigate the ascending chain conditions on principal left and right ideals for semidirect products of semigroups and show how this is connected to the corresponding problem for rings of skew generalized power series. Let S be a left cancellative semigroup with a unique idempotent e, T a right cancellative semigroup with an idempotent f and $\omega: T \to \operatorname {End}(S)$ a semigroup homomorphism such that ??(f)=id _S . We show that in this case the semidirect product S? _?? T satisfies the ascending chain condition for principal left ideals (resp. right ideals) if and only if S and T satisfy the ascending chain condition for principal left ideals (resp. right ideals and $\operatorname {Im}\omega(t)$ is closed for complete inverses for all t??T). We also give several examples to show that for more general semigroups these implications may not hold.     

A remark on a paper of B. R. Gelbaum

Summary In this paper the following generalization of a theorem by B.R. Gelbaum is proved:Let (K, d) be a compact, connected metric space. Let B denote the Borel sets of (K, d), and P be a probability measure on B with P(G)O for any nonempty open G, f, gC(K,d) independent random variables on (K,B,P) and let g satisfy the following assumption:There is an y _o such that g ^–1(y₀) is a finite nonempty set. Then f is a constant function.Examples show that the assumptions of this theorem are essential.     

Modules Satisfying the S-Noetherian Property and S-ACCR

Let A = k[x₁,..., x_n] be a standard graded k-algebra over an infinite field k. We assume A is Cohen-Macaulay and has Krull dimension one. Let e denote the multiplicity of A and r - 1 the postulation number of A. Let I be a homogeneous ideal in A of grade one. Let j(I) denote the smallest degree of a regular form in I. Let l (I) denote the smallest power of (x₁,... , x_n) contained in I. If μ(I) denotes the minimum number of generators of I, then we show μ(I) ≤ e + j(I) - max{r,l(I)}, We then show how Dubreil's Second Theorem follows easily from this inequality     

On the distribution of norms of prime ideals of a given class in arithmetic progressions

Let C be a class of ideals of the ring of algebraic numbers of an imaginary quadratic field. Let l and q be relatively prime integers, , and A₁ τ; 1. An asymptotic formula for the number π₁(x, q, l, C) of prime ideals belonging to the class C whose norms do not exceed x and lie in an arithmetic progression is obtained in this paper. Bibliography: 6 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 322, 2005, pp. 45–62.     

Partial differential equations without solution operators in weighted spaces of (generalized) functions

Let P(D) be a hypoelliptic pdo with constant coefficients and let E(M) (and(W_{M, b}) be the weighted spaces of C-functions (resp. of distributions) defined by Palamodov (resp. Gelfand/Shilov), where M is a radially symmetric weight function, eventually satisfying some mild technical conditions. Then P(D) has no continuous linear right inverse in E(M). If the index of hypoellipticity w.r.t. some x is greater than 1 and is minimal in a certain sense, then P(D) has no right inverse in (W_M,)_b.If P(D) is elliptic however, then a continuous linear right inverse for P(D) exists in (W_M,)_b.     

Hankel operators on planar domains

Let Ω be a bounded domain in the plane whose boundary consists of a finite number of disjoint analytic simple closed curves LetA denote the space of analytic functions on Ω which are square integrable over Ω with respect to area measure and letP denote the orthogonal projection ofL ²(Ω,dA) ontoA. A functionb inA induces a Hankel operator (densely defined) onA by the ruleH _b (g)=(I?P)bg. This paper continues earlier investigations of the authors and others by determining conditions under whichH _b is bounded, compact, or lies in the Schatten-von Neumann idealS _p , 1<p<∞     

On rationalized H- and co-H-spaces with an appendix on decomposable H- and co-H-spaces

Let R be a subring of the rationals with 1/2, 1/3R; let S _R ⁿ denote the R-local n-sphere and define _R ⁿ :=S _R ⁿ for n odd, _R ⁿ :=S _R ⁿ for n>0 even. An H-space (resp. a 1-conn. co-H-space) is decomposable over R, if it is homotopy equivalent to a weak product of spaces _R ⁿ (resp. to a wedge of R-local spheres). We prove that, if E is grouplike decomposable of finite type over R, the functor [-,E] is determined on finite dim. complexes by the Hopf algebra M^*(E;R); here M^* denotes the unstable cohomotopy functor of H.J. Baues. If C is cogrouplike decomposable over R, the functor [C,-] is determined on 1-conn. R-local spaces by _*(C) as a cogroup in the category of M-Lie algebras. For R = the functor [-,E] is also determined by the Lie algebra _*(E) and [C,-] by the Berstein coalgebra associated to the comultiplication of C.     

On finiteness conditions for Rees matrix semigroups

Let T=[S; I; J; P] be a Rees matrix semigroup where S is a semigroup, I and J are index sets, and P is a J × I matrix with entries from S, and let U be the ideal generated by all the entries of P. If U has finite index in S, then we prove that T is periodic (locally finite) if and only if S is periodic (locally finite). Moreover, residual finiteness and having solvable word problem are investigated.