Generators and factorisations of transformation semigroups

If E is the set of idempotents and G the group of units within a full transformation semigroup ℐ x , then EG = GE = ℐ x if X is finite. The question of identifying the subsemigroup EG = GE = 〈G∪E〉 in the case where X is infinite leads to an investigation of interrelations among various naturally occurring subsemigroups of ℐ X . In the final section it is shown that precisely two additional elements µ, v are needed in order that G∪E∪{µ, v} should generate ℐ x .