Regular solutions of language inequalities and well quasi-orders

By means of constructing suitable well quasi-orders of free monoids we prove that all maximal solutions of certain systems of language inequalities are regular. This way we deal with a wide class of systems of inequalities where all constants are languages recognized by finite simple semigroups. In a similar manner we also demonstrate that the largest solution of the inequality XK⊆LX is regular provided the language L is regular.