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 X K C L X is regular provided the language L is regular. (c) 2005 Elsevier B.V. All rights reserved.
well quasi-order finite simple semigroup language equation regular language syntactic semigroup