卷 57, 编号 2 (2018)

The notion of an exponential R-group, where R is an arbitrary associative ring with unity, was introduced by R. Lyndon. A. G. Myasnikov and V. N. Remeslennikov refined this notion by adding an extra axiom. In particular, the new notion of an exponential MR-group is an immediate generalization of the notion of an R-module to the case of noncommutative groups. Basic concepts in the theory of exponential MR-groups are presented, and we propose a particular method for constructing tensor completion—the key construction in the category of MR-groups. As a consequence, free MR-groups and free MR-products are described using the language of group constructions.

It is shown that the Gruenberg–Kegel graph of a finite almost simple group is equal to the Gruenberg–Kegel graph of some finite solvable group iff it does not contain 3-cocliques. Furthermore, we obtain a description of finite almost simple groups whose Gruenberg–Kegel graphs contain no 3-cocliques.

We complete the classification of edge-symmetric distance-regular coverings of complete graphs with r /∉ {2, k, (k − 1)/μ} for the case of the almost simple action of an automorphism group of a graph on a set of its antipodal classes; here r is the order of an antipodal class.