Cofinality of the nonstationary ideal

We show that the reduced cofinality of the nonstationary ideal on a regular uncountable cardinal may be less than its cofinality, where the reduced cofinality of is the least cardinality of any family of nonstationary subsets of such that every nonstationary subset of can be covered by less than many members of . For this we investigate connections of the various cofinalities of with other cardinal characteristics of and we also give a property of forcing notions (called manageability) which is preserved in -support iterations and which implies that the forcing notion preserves non-meagerness of subsets of (and does not collapse cardinals nor changes cofinalities).

     

Repetitive algebras of iterated tilted algebras

In this article, we prove that the repetitive algebra of an iterated tilted algebra can be realized by the repetitive algebra of some tilted algebra. In particular, an iterated tilted algebra can be obtained by a series of reflections from some tilted algebra. Project supported by the National Natural Science Fund of China     

Bordism of algebras over Hopf algebras

An algebraic theory of bordism via characteristic numbers, analogous to topological bordism, is given. The Steenrod algebra is replaced by a fairly general graded Hopf algebra A, topological spaces by algebras over A, vector bundles by Thom modules, and closed manifolds by Poincaré algebras over A.     

Schur algebras of Brauer algebras I

Schur algebras of Brauer algebras are defined as endomorphism algebras of certain direct sums of ‘permutation modules’ over Brauer algebras. Explicit combinatorial bases of these new Schur algebras are given; in particular, these Schur algebras are defined integrally. The new Schur algebras are related to the Brauer algebra by Schur–Weyl dualities on the above sums of permutation modules. Moreover, they are shown to be quasi-hereditary. Over fields of characteristic different from two or three, the new Schur algebras are quasi-hereditary 1-covers of Brauer algebras, and hence the unique ‘canonical’ Schur algebras of Brauer algebras.     

Nijenhuis algebras, NS algebras, and N-dendriform algebras

In this paper, we study (associative) Nijenhuis algebras, with emphasis on the relationship between the category of Nijenhuis algebras and the categories of NS algebras and related algebras. This is in analogy to the well-known theory of the adjoint functor from the category of Lie algebras to that of associative algebras, and the more recent results on the adjoint functor from the categories of dendriform and tridendriform algebras to that of Rota-Baxter algebras. We first give an explicit construction of free Nijenhuis algebras and then apply it to obtain the universal enveloping Nijenhuis algebra of an NS algebra. We further apply the construction to determine the binary quadratic nonsymmetric algebra, called the N-dendriform algebra, that is compatible with the Nijenhuis algebra. As it turns out, the N-dendriform algebra has more relations than the NS algebra.     

Rota-Baxter algebras and dendriform algebras

In this paper we study the adjoint functors between the category of Rota-Baxter algebras and the categories of dendriform dialgebras and trialgebras. In analogy to the well-known theory of the adjoint functor between the category of associative algebras and Lie algebras, we first give an explicit construction of free Rota-Baxter algebras and then apply it to obtain universal enveloping Rota-Baxter algebras of dendriform dialgebras and trialgebras. We further show that free dendriform dialgebras and trialgebras, as represented by binary planar trees and planar trees, are canonical subalgebras of free Rota-Baxter algebras.     

Baxter algebras and Hopf algebras

By applying a recent construction of free Baxter algebras, we obtain a new class of Hopf algebras that generalizes the classical divided power Hopf algebra. We also study conditions under which these Hopf algebras are isomorphic.

     

Symplectic algebras and poisson algebras

Abstract

A ring R is called left P-injective if for every a ∈ R, aR = r(l(a)) where l( ? ) and r( ? ) denote left and right annihilators respectively. The ring R is called left GP-injective if for any 0 ≠ a ∈ R, there exists n > 0 such that a ⁿ  ≠ 0 and a ⁿ R = r(l(a ⁿ )). As a response to an open question on GP -injective rings, an example of a left GP-injective ring which is not left P-injective is given. It is also proved here that a ring R is left FP -injective if and only if every matrix ring 𝕄 _n (R) is left GP-injective.     

Hopf algebras over hopf algebras

Summary In any category with products and a terminal object one may define the notions of group, module over a group etc. if f: R′→R is a homomorphism of groups, and M an R-module, then one has an induced R′-module f*(M). If one is working in the category of sets, one may define a functor left adjoint to f* by N→R⊗_R′ N, where N is an R′-module. In this paper we show that f* has a left adjoint when one is working in the category of graded connected coalgebras over a field.     

Left-symmetric algebras of derivations of free algebras

A structure of a left-symmetric algebra on the set of all derivations of a free algebra is introduced such that its commutator algebra becomes the usual Lie algebra of derivations. Left and right nilpotent elements of left-symmetric algebras of derivations are studied. Simple left-symmetric algebras of derivations and Novikov algebras of derivations are described. It is also proved that the positive part of the left-symmetric algebra of derivations of a free nonassociative symmetric m-ary algebra in one free variable is generated by one derivation and some right nilpotent derivations are described.     

Monounary algebras and bottleneck algebras

This paper deals with representations of monounary algebras by bottleneck algebras (b-representations). Necessary and sufficient conditions for a monounary algebra to have a b-representation are found: In particular, it is shown that each finite monounary algebra is b-representable. Received June 25, 1997; accepted in final form June 11, 1998.     

Modified Ringel-Hall algebras,naive lattice algebras and lattice algebras

For a given hereditary abelian category satisfying some finiteness conditions, in certain twisted cases it is shown that the modified Ringel-Hall algebra is isomorphic to the naive lattice algebra and there exists an epimorphism from the modified Ringel-Hall algebra to the lattice algebra. Furthermore, the kernel of this epimorphism is described explicitly. Finally, we show that the naive lattice algebra is invariant under the derived equivalences of hereditary abelian categories.     

Decompositions of universal algebras by idempotent algebras

An algebra with units is an algebra in which every subalgebra contains a singleton subalgebra. A one-unit-algebra is an algebra in which every subalgebra contains exactly one singleton subalgebra. IfU,V are subclasses of a classK of algebras,U _K V is the class of all K on which there is a congruence such that /V and every -class that is a subalgebra of belonging toK belongs also toU, e.g., ifK is the class of all semigroups,V is the class of all bands andU is the class of all groups,U _K V is the class of all bands of groups. We studyU _K V andU _K U whereU is a class of one-unit-K-algebras andV is a class of idempotentK-algebras. IfK is a class of algebras of type closed under subalgebras and homomorphisms,U is the class of all one-unit-K-algebras andV is the class of all idempotentK-algebras, thenU _K V is the class of allK-algebras that are -reducts of , e-algebras satisfying e(x) is a singleton subalgebra for everyx A belonging to the -subalgebra of generated byx and e(f(– x₁, x₂,..., x_n))=e(fe(x₁), e(x₂),..., e(x_n)) for every n-ary operationf of type . IfK is a variety of algebras with units and of finite type,U andV are finitely based (relative toK) subquasivarieties ofK, thenU _K V is finitely based relative toK. IfK is the variety of all commutative groupoids with an additional unary operatione satisfying e(e(x))=e(x)=e(x)· e(x), e(x · y)=e(x)· e(y),U andV are the subvarities ofK defined by e(x)=e(y) andx=e(x) respectively, thenU _K U is neither a variety nor finitely based. Some applications to semigroups and quasigroups are considered.Presented by G. Grätzer.