The Levi classes generated by nilpotent groups

Given an arbitrary class M of groups, denote by L(M) the class of all groups G in which the normal closure of every element belongs to M. Consider the quasivariety _q F _p generated by the relatively free group in the class of nilpotent groups of length at most 2 with the commutant of exponent p (where p is an odd prime). We describe the Levi class that is generated by qF _p.     

Finite groups generated by two nilpotent subgroups

Some criteria for the solvability of ABA groups with nilpotent subgroups A and B of special form are proved. An ABA group is a group of the form G = ABA, where A and B are subgroups of the group G.Translated from Matematicheskie Zametki, Vol. 11, No. 3, pp. 293–298, March, 1972.     

Semigroups of transformations restricted by an equivalence

Suppose σ is an equivalence on a set X and let E(X, σ) denote the semigroup (under composition) of all α: X → X such that σ ⊆ α ∘ α ⁻¹. Here we characterise Green’s relations and ideals in E(X, σ). This is analogous to recent work by Sullivan on K(V, W), the semigroup (under composition) of all linear transformations β of a vector space V such that W ⊆ ker β, where W is a fixed subspace of V.     

Semigroups generated by a group and an idempotent

It is well known that the semigroup of all transformations on a finite set X of order n is generated by its group of units, the symmetric group, and any idempotent of rank n ? 1. Similarly, the symmetric inverse semigroup on X is generated by its group of units and any idempotent of rank n ? 1 while the analogous result is true for the semigroup of all n × n matrices over a field.

In this paper we begin a systematic study of the structure of a semigroup S generated by its group G of units and an idempotent ? . The first section consists of preliminaries while the second contains some general results which provide the setting for those which follow.

In the third section we shall investigate the situation where G is a permutation group on a set X of order n and ? is an idempotent of rank n ? 1. In particular, we shall show that any such semigroup S is regular. Furthermore we shall determine when S is an inverse or orthodox semigroup or completely regular semigroup.

The fourth section deals with a special case, that in which G is cyclic. The fifth, and last, deals with the situation where G is dihedral. In both cases, the resulting semigroup has a particularly delicate structure which is of interest in its own right. Both situations are replete with interesting combinatorial gems.

The author was led to the results of this paper by considering the output of a computer program he was writing for generating and analyzing semigroups.     

On the variety generated by all nilpotent lattice-ordered groups

In 1974, J. Martinez introduced the variety of weakly Abelian lattice-ordered groups; it is defined by the identity

     

Dominions in finitely generated nilpotent groups

In the first part, we prove that the dominion (in the sense of Isbell) of a subgroup of a finitely generated nilpotent group is trivial in the category of all nilpotent groups. In the second part, we show that the dominion of a subgroup of a finitely generated nilpotent group of class two is trivial in the category of all metabelian nilpotent groups.     

Semigroups generated by pseudo-contractive mappings under the Nagumo condition

Let X be a Banach space whose dual space X^∗ is uniformly convex. We demonstrate that, for any demicontinuous, weakly Nagumo, k-pseudo-contractive mapping T:D(T)⊆X→X with closed domain, A=T−I weakly generates a semigroup on D(T). In this paper, we project the consequences of this result on fixed point theory. In particular, we show that if k<1 (id est, if T is strongly pseudo-contractive), then T has a unique fixed point. This implies that, if T is pseudo-contractive (k=1) and D(T) is closed, bounded, and convex, then T has at least one fixed point. Consequently, any demicontinuous pseudo-contractive mapping T:C→C (for an appropriate C) has a fixed point, which has been an important open question in fixed point theory for quite some time. In a subsequent paper, we explore the consequences of the semigroup result on the existence of solutions to certain partial differential equations. The semigroup result directly implies the existence of unique global solutions to time evolution equations of the form u^′=Au where A is a combination of derivatives. The fixed point results from this paper imply the existence of solutions to partial differential equations of the form Lu=f.     

Rational sets in finitely generated nilpotent groups

We deal with a class of rational subsets of a group, that is, the least class of its subsets which contains all finite subsets and is closed under taking union. a product of two sets, and under generating of a submonoid by a set. It is proved that the class of rational subsets of a finitely generated nilpotent group G is a Boolean algebra iff G is Abelian-by-finite. We also study the question asking under which conditions the set of solutions for equations in groups will be rational. It is shown that the set of solutions for an arbitrary equation in one variable in a finitely generated nilpotent group of class 2 is rational. And we give an example of an equation in one variable in a free nilpotent group of nilpotency class 3 and rank 2 whose set of solutions is not rational. Supported by RFFR grant No. 98-01-00932. Translated fromAlgebra i Logika, Vol. 39, No. 4, pp. 379–394, July–August, 2000.     

Irreducible representations of finitely generated nilpotent torsion-free groups

An investigation of the structure of the quotient algebra, with respect to a prime ideal, of the group algebra of a finitely-generated nilpotent torsion-free group. Conditions are studied under which an irreducible representation of such a group is induced.Translated from Matematicheskie Zametki, Vol. 9, No. 2, pp. 199–210, February, 1971.     

On monomial representations of finitely generated nilpotent groups

A result of Segal states that every complex irreducible representation of a finitely generated nilpotent group G is monomial if and only if G is abelian-by-finite. A conjecture of Parshin, recently proved affirmatively by Beloshapka and Gorchinskii (2016), characterizes the monomial irreducible representations of finitely generated nilpotent groups. This article gives a slightly shorter proof of the conjecture using ideas of Kutzko and Brown. We also give a characterization of the finite-dimensional irreducible representations of two-step nilpotent groups and describe these completely for two-step groups whose center has rank one.     

Semigroups of partial transformations with kernel and image restricted by an equivalence

Semigroup Forum - For an arbitrary set X and an equivalence relation $$mu$$ on X, denote by $$P_mu (X)$$ the semigroup of partial transformations $$alpha$$ on X such that $$xmu subseteq x(ker...