Abstract:
In this paper, we consider the operation of unambiguous multiplication of formal languages. It can be derived from the regular language concatenation by restricting the words of resulting language to be unambiguously represented as concatenations of words from the factor languages. A full characterization of $\otimes$-factorizations of a free monoid over a singleton generator is given. The existence of a representation of a free monoid as an unambiguous multiplication of languages that are not recursively enumerable is derived as a corollary.
Key words:formal languages, unambiguous concatenation of formal languages, language factorization, free monoid, mixed radix numeral systems.
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