Semitransitive subsemigroups of the singular part of the finite symmetric inverse semigroup

We prove that the minimal cardinality of a semitransitive subsemigroup in the singular part $\mathcal{I}_{n}\setminus \mathcal{S}_{n}$ of the symmetric inverse semigroup $\mathcal{I}_{n}$ is 2n?p+1, where p is the greatest proper divisor of n, and classify all semitransitive subsemigroups of this minimal cardinality.     

全变换半群中的一种扩张方法

设e是集中Ω上的全变换半群TΩ的一个幂等元,X是e的像集,G是X上的对称群Sx的子群,本文给出一种方法,通过e把G扩张成TΩ的一个纯正子半群（orthodox）。     

Small Transitive Families of Subspaces

A family of subspaces of a complex separable Hilbert space is transitive if every bounded operator which leaves each of its members invariant is scalar. This article surveys some results concerning transitive families of small cardinality, and adds some new ones. The minimum cardinality of a transitive family in finite dimensions (greater than 2) is 4. In infinite dimensions a transitive pair of linear manifolds exists but the minimum cardinality of a transitive family of dense operator ranges or norm-closed subspaces is not known. However, a transitive family of dense operator ranges with 5 elements can be found, and so can a transitive family of norm-closed subspaces with 4 elements. In finite dimensions (> 1) three nest algebras (corresponding to maximal nests) can intersect in the scalar operators, but two cannot. It is not known if this is the case in infinite dimensions for maximal nests of type ω + 1. Four such nest algebras can intersect in the scalar operators. Received June 15, 2002, Accepted November 27, 2002     

A classification of maximal subsemigroups of finite order-preserving transformation semigroups

We describe the maximal subsemigroups of the semigroup of all order-preserving transformations of a finite chain and completely obtain their classification. We also count the number of its maximal subsemigroups.     

有限部分保序变换半群POn的具有某种性质的极大子半群

本文研究了有限链上的部分保序变换半群Pon.通过对其幂等元的分析,获得TPOn的极大正则子半群和极大幂等元生成子半群的结构与分类.     

The Commutativity Relation in the Symmetric Semigroup

We compute the cardinality of the centralizer of an injection or surjection provided that the basic set is countable. We prove a formula for the cardinality of the set of conjugacy classes in the infinite symmetric group.     

PO_n的局部极大幂等元生成的子半群

研究了有限链上的部分保序变换半群PO_n.通过对其幂等元的分析,获得了PO_n的局部极大幂等元生成的子半群的结构与分类.     

Inverse subsemigroups and classes of finite aperiodic semigroups

We prove a number of results related to finite semigroups and their inverse subsemigroups, including the following. (1) A finite semigroup is aperiodic if and only if it is a homomorphic image of a finite semigroup whose inverse subsemigroups are semilattices. (2) A finite inverse semigroup can be represented by order-preserving mappings on a chain if and only if it is a semilattice. Finally, we introduce the concept of pseudo-small quasivariety of finite semigroups, generalizing the concept of small variety.     

Balanced subsets of a symmetric inverse semigroup

For elements in the subsets of some symmetric inverse semigroup we study the problem of equal cardinality for the sets of commuting and noncommuting elements.     

Structure of Partially Ordered Cyclic Semigroups

This paper recalls some properties of a cyclic semigroup and examines cyclic subsemigroups in a finite ordered semigroup. We prove that a partially ordered cyclic semigroup has a spiral structure which leads to a separation of three classes of such semigroups. The cardinality of the order relation is also estimated. Some results concern semigroups with a lattice order.     

On free semigroups of automaton transformations

It is established that the subset of freek-generated subsemigroups of the semigroup of all automaton transformations over a finite alphabet is a second category set (in the sense of the Baire category approach) in the set of allk-generated subsemigroups. A continuum series of pairs of automaton transformations each of which generates a free semigroup of rank two is indicated. A criterion is established for this semigroup to be a finite-automaton group. Translated fromMatematicheskie Zametki, Vol. 63, No. 2, pp. 248–259, February, 1998. The author wishes to express his deep gratitude to Professor V. I. Sushchans'kii for permanent help and attention to the research. This research was partially supported by the ISSEP under grant No. GSU 051341.     

Containment for c, s, t operators on a binary relation

The operators c, s and t are complement, symmetric and transitive closure of a binary relation. If u and v denote finite sequences of these operators then we define u v iff for every binary relation . We find the distinct representative and containment between these sequences. The asymmetric operator is not one of these. There are 54 representatives for binary relations, 20 for transitive relations, and 10 for symmetric relations. There are 26 component types of a binary relation, 10 for transitive relations, and 6 for symmetric relations. There are 16 connected types of a binary relation, 8 for transitive relations, and 4 for symmetric relations. We study well founded relations. Total relations may not be contractible but well founded ones are. The complement of (a Hasse diagram of) a non-empty partial order of arbitrary cardinality is contractible. Ordered sets are naturally homotopy equivalent to partially ordered sets. There are 10 relations which can have arbitrary polyhedral homotopy type and 42 are either contractible or the homotopy type of a wedge of n-spheres. The homotopy type of two relations is not determined.     

半群K(n,r)中的幂等生成元

设Singn是由一个n元集上的所有奇异变换所构成的奇异变换半群，I是由Singn中一些亏数为1的幂等元组成的集合，Howie利用有向图证明了：I是Singn的一个生成集当且仅当与其相应的有向图D（I）是强连通的完全图，本文利用多重有向图将这一结果推广到Singn的每个理想K（,r)上。     

Maximal properties of some subsemigroups in finite order-preserving transformation semigroups

Let [n] = {1,2,…,n} be a finite set, ordered in the usual way. The order-preserving transformation semigroup O_n is the set of all order-preserving transformations of [n] (excluding the identity mapping) under composition. In this paper we first describe maximal idempotent-generated subsemigroups of O _n, and show that O_n has 2n - 2 such subsemi-groups. Secondly, we investigate maximal regular subsemigroups of O_n , and obtain the number of such subsemigroups as 2n - 3. Thirdly, we describe maximal idempotent-generated regular subsemigroups of O_n , and also obtain their classification and number.     

Cyclic subsemigroups of symmetric inverse semigroups

A generalization of the cycle notation for permutations is introduced for partial one-one transformations (charts). Notational representation theorems for charts that generalize those of permutations are given. Notational multiplication of charts is developed and then applied to yield a transparent proof of Frobenius' result which bounds the idempotent in the cyclic subsemigroup. Lastly, the well known result that the structure of the cyclic subgroups of the finite symmetric groups is determined from combinations of disjoint cycles is generalized to the cyclic subsemigroups of the finite symmetric inverse semigroups.     

On the Structure of IO n

Abstract. We study the structure of the semigroup IO _n of all order-preserving partial bijections on an n -element set. For this semigroup we describe maximal subsemigroups, maximal inverse subsemigroups, automorphisms and maximal nilpotent subsemigroups. We also calculate the maximal cardinality for the nilpotent subsemigroups in IO _n which happens to be given by the n -th Catalan number.     

Fuzzy implication operators for difference operations for fuzzy sets and cardinality-based measures of comparison

In this paper, we determine by means of fuzzy implication operators, two classes of difference operations for fuzzy sets and two classes of symmetric difference operations for fuzzy sets which preserve properties of the classical difference operation for crisp sets and the classical symmetric difference operation for crisp sets respectively. The obtained operations allow us to construct as in [B. De Baets, H. De Meyer, Transitivity-preserving fuzzification schemes for cardinality-based similarity measures, European Journal of Operational Research 160 (2005) 726–740], cardinality-based similarity measures which are reflexive, symmetric and transitive fuzzy relations and, to propose two classes of distances (metrics) which are fuzzy versions of the well-known distance of cardinality of the symmetric difference of crisp sets.     

Cone-transitive matrix semigroups

Semigroups of matrices (over an ordered field) with non-negative entries are considered. A complete characterization is obtained for the semigroups which are minimal transitive on the positive (or non-negative) cone of the underlying vector space. Consequently, an explicit form for the semigroups sharply transitive on the cone is derived.