Theorem 9 Let (S, .,≤) be an ordered semigroup. If S is a union of left
strongly simple subsemigroups of S, then every left ideal of S is an intra-regular
subsemigroup of S. ”Conversely”, if every left ideal of S is an intra-regular
subsemigroup of S, then S is a complete semilattice of left strongly simple
semigroups.