Some types of congruences in semigroups

The book containing four chapters is devoted congruences of some types in semigroups (we study certain congruences on very wide classes of semi- groups such that the quotient semigroups belong to most important classes of semigroups). In this book are described matrix congruences group congruences rectangular group congruences Clifford congruences E-unitary congruences UBG-congruences OBG-congruences etc. on certain semigroups with very big classes of semigroups (e.g. E-inversive semigroups eventually regular semigroups structurally regular semigroups idempotent-surjective semigroups).