Words Guaranteeing Minimum Image
| Autor: | Margolis, S. W., Pin, J. -E., Volkov, M. V. |
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| Jazyk: | angličtina |
| Rok vydání: | 2004 |
| Zdroj: | Int. J. Found. Comput. Sci. International Journal of Foundations of Computer Science |
| Popis: | Given a positive integer n and a finite alphabet Σ, a word w over Σ is said to guarantee minimum image if, for every homomorphism φ from the free monoid Σ* over Σ into the monoid of all transformations of an n-element set, the range of the transformation wφ has the minimum cardinality among the ranges of all transformations of the form vφ where v runs over Σ*. Although the existence of words guaranteeing minimum image is pretty obvious, the problem of their explicit description is very far from being trivial. Sauer and Stone in 1991 gave a recursive construction for such a word w but the length of their word was doubly exponential (as a function of n). We first show that some known results of automata theory immediately lead to an alternative construction that yields a simpler word that guarantees minimum image: it has exponential length, more precisely, its length is O(|Σ|(n3-n)). Then with some more effort, we find a word guaranteeing minimum image similar to that of Sauer and Stone but of length O(|Σ|(n2-n)). On the other hand, we prove that the length of any word guaranteeing minimum image cannot be less than |Σ|n-1. © 2004 World Scientific Publishing Company. |
| Databáze: | OpenAIRE |
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