Primary elements in Prüfer lattices

In this paper we study primary elements in Prüfer lattices and characterize -lattices in terms of Prüfer lattices. Next we study weak ZPI-lattices and characterize almost principal element lattices and principal element lattices in terms of ZPI-lattices.     

Characterizations of Standard Elements in Posets

The fundamental characterization theorem of standard elements in lattices is extended to posets. Several other characterizations of standard elements are obtained in a sectionally semi-complemented poset and also in an atomistic, dually sectionally semi-complemented poset.     

Noetherian lattices in which every element is a product of primary elements

We characterize those Noetherian lattices in which every element is a product of primary elements.     

Characteristic Elements of Unimodular -lattices

Characteristic elements have been useful in the classification of unimodular lattices over the integers. This article gives an explicit formula for characteristic elements of a lattice in terms of a basis for the lattice and the dual of that basis.     

Characteristic Elements of Unimodular -lattices

Characteristic elements have been useful in the classification of unimodular lattices over the integers. This article gives an explicit formula for characteristic elements of a lattice in terms of a basis for the lattice and the dual of that basis.     

Dilworth's principal elements

Principal elements were introduced in multiplicative lattices by R. P. Dilworth, following an earlier but less successful attempt in the joint work of Ward and Dilworth. As suggested by their name, principal elements are the analogue in multiplicative lattices of principal ideals in (commutative) rings. Principal elements are the cornerstone on which the theory of multiplicative lattices and abstract ideal theory now largely rests. In this paper, we obtain some new results regarding principal elements and extend some others. In addition, we try to convey what is known and what is not known about the subject. We conclude with a fairly extensive (but likely not exhaustive) bibliography on principal elements.Dedicated to R. P. DilworthPresented by E. T. Schmidt.     

On characterizations of atomistic lattices

In the present paper we characterize atomistic lattices. These characterizations are given in terms of concepts related to pure elements (cf. [4], [6]) and neat elements (cf. [3]).     

\mathcal{l} -prime elements in multiplicatice lattices

In this paper we study -prime elements in C-lattices and characterize Prüfer lattices, almost principal element lattices and principal element lattices in terms of -prime elements. Using these results, some new characterizations are given for general ZPI-rings and almost multiplication rings. Finally some new equivalent conditions are given for Dedekind lattices. Received August 18, 2000; accepted in final form April 22, 2002.     

Combinatorial representation and convex dimension of convex geometries

We develop a representation theory for convex geometries and meet distributive lattices in the spirit of Birkhoff's theorem characterizing distributive lattices. The results imply that every convex geometry on a set X has a canonical representation as a poset labelled by elements of X. These results are related to recent work of Korte and Lovász on antimatroids. We also compute the convex dimension of a convex geometry.Supported in part by NSF grant no. DMS-8501948.     

Algebraic lattices and nonassociative structures

Uniform elements in algebraic lattices are studied and their relationship with some nonassociative extensions of Goldie's Second Theorem is shown.

     

Finite distributive nearlattices

Our main goal is to develop a representation for finite distributive nearlattices through certain ordered structures. This representation generalizes the well-known representation given by Birkhoff for finite distributive lattices through finite posets. We also study finite distributive nearlattices through the concepts of dual atoms, boolean elements, complemented elements and irreducible elements. We prove that the sets of boolean elements and complemented elements form semi-boolean algebras. We show that the set of boolean elements of a finite distributive lattice is a boolean lattice.     

Infinite joins that are finitely join-irreducible

Complete lattices are studied which contain an element u which is not the join of a finite set of smaller elements, but is the join of all elements <u.This work was done while the first author was partly supported by NSF contract DMS 85-02330; during the completion of the article the second author was partly supported by NSF grant DMS 88-07043.     

Decomposition of partial orders

A decomposition theory for partial orders which arises from the split decomposition of submodular functions is introduced. As a consequence of this theory, any partial order has a unique decomposition consisting of indecomposable partial orders and certain highly decomposable partial orders. The highly decomposable partial orders are completely characterized. As a special case of partial orders, we consider lattices and distributive lattices. It occurs, that the highly decomposable distributive lattices are precisely the Boolean lattices.     

Reflections of Root Lattices for Kac–Moody Algebras

In the present paper we determine all the elements in the root lattices of symmetrizable Kac–Moody algebras whose reflections preserve the root systems. Also we discuss elements in the root lattices whose reflections preserve the root lattices.     

Special Elements of the Lattice of Overcommutative Varieties of Semigroups

The distributive, codistributive, standard, costandard, and neutral elements of the lattice of overcommutative varieties of semigroups are completely described.     

Reducibility number

Let P be a poset in a class of posets P. A smallest positive integer r is called reducibility number of P with respect to P if there exists a non-empty subset S of P with |S|=r and P-S∈P. The reducibility numbers for the power set 2ⁿ of an n-set (n?2) with respect to the classes of distributive lattices, modular lattices and Boolean lattices are calculated. Also, it is shown that the reducibility number r of the lattice of all subgroups of a finite group G with respect to the class of all distributive lattices is 1 if and only if the order of G has at most two distinct prime divisors; further if r is a prime number then order of G is divisible by exactly three distinct primes. The class of pseudo-complemented u-posets is shown to be reducible. Deletable elements in semidistributive posets are characterized.     

The Dedekind-MacNeille completion as a reflector

We introduce a special type of order-preserving maps between quasiordered sets, the so-called cut-stable maps. These form the largest morphism class such that the corresponding category of quasiordered sets contains the category of complete lattices and complete homomorphisms as a full reflective subcategory, the reflector being given by the Dedekind-MacNeille completion (alias normal completion or completion by cuts). Suitable restriction of the object class leads to the category of separated quasiordered sets and its full reflective subcategory of completely distributive lattices. Similar reflections are obtained for continuous lattices, algebraic lattices, etc.     

How small can a lattice of order-dimension n be?

The aim of this paper is to study the order-dimension of partition lattices and linear lattices. Our investigations were motivated by a question due to Bill Sands: For a lattice L, does dim L=n always imply |L|≥2 ⁿ ? We will answer this question in the negative since both classes of lattices mentioned above form counterexamples. In the case of the partition lattices, we will determine the dimension up to an absolute constant. For the linear lattice over GF(2), L _n , we determine the dimension up to a factor C/n for an absolute constant C.     

On a theorem of Cantor-Bernstein type for algebras

Freytes proved a theorem of Cantor-Bernstein type for algbras; he applied certain sequences of central elements of bounded lattices. The aim of the present paper is to extend the mentioned result to the case when the lattices under consideration need not be bounded; instead of sequences of central elements we deal with sequences of internal direct factors of lattices. This work was supported by Science and Technology Assistance Agency under the contract No APVT-51-032002.     

Weakly Orthomodular and Dually Weakly Orthomodular Lattices

We introduce so-called weakly orthomodular and dually weakly orthomodular lattices which are lattices with a unary operation satisfying formally the orthomodular law or its dual although neither boundedness nor complementation is assumed. It turns out that lattices being both weakly orthomodular and dually weakly orthomodular are in fact complemented but the complementation need not be neither antitone nor an involution. Moreover, every modular lattice with complementation is both weakly orthomodular and dually weakly orthomodular. The class of weakly orthomodular lattices and the class of dually weakly orthomodular lattices form varieties which are arithmetical and congruence regular. Connections to left residuated lattices are presented and commuting elements are introduced. Using commuting elements, we define a center of such a (dually) weakly orthomodular lattice and we provide conditions under which such lattices can be represented as a non-trivial direct product.