Green’s equivalences; regular semigroups
John M Howie · 1995
Abstract The notion of ideal mentioned in the last chapter leads naturally to the consideration of certain equivalence relations on a semigroup. These equivalences, first studied by J. A. Green (1951), have played a fundamental role in the development of semigroup theory. They are concerned with mutual divisibility of various kinds, and all of them reduce to the universal equivalence in a group.