Abstract
Roughly, a faithful (resp. bifaithful) rational transduction is a non deterministic finite state mapping that does not decrease (resp. alter) the length of words by very much. We introduce the notion of stronglyf-saturated language:L is stronglyf-saturated if and only if for any languageL′, from which we can obtainL by faithful rational transduction, for any languageL″, image ofL by a faithful rational transduction, there exists a bifaithful rational transduction τ such thatL″ is the image ofL′ τ. We prove that no quasirational language and no language in the substitution closed rational cone generated by bounded languages is stronglyf-saturated. Conversely, we establish that a language such as\(\bar D_1^{\prime *} = \{ w \in \{ a,b\} ^* /|w|_a \ne |w|_b \}\), very low in the hierarchy of algebraic languages, is stronglyf-saturated thus is not a quasirational language. We also establish that any commutative quasi rational language over two letters is rational.
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Latteux, M., Leguy, J. On the usefulness of bifaithful rational cones. Math. Systems Theory 18, 19–32 (1985). https://doi.org/10.1007/BF01699459
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DOI: https://doi.org/10.1007/BF01699459