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The equivalence of mappings on languages. (English) Zbl 0637.68093
Trends, techniques, and problems in theoretical computer scinece, 4th Int. Meet. Young Comput. Sci., Smolenice/Czech. 1986, Lect. Notes Comput. Sci. 281, 26-38 (1987).
[For the entire collection see Zbl 0633.00024.]
We define the notion of the equivalence of mappings on languages in three different ways and call them universal equivalence, existential equivalence and equivalence with multiplicities. We survey recent results on this topic, as well as state some open problems.

68Q45 Formal languages and automata
20M35 Semigroups in automata theory, linguistics, etc.