Equality languages and fixed point languages

Joost Engelfriet; Grzegorz Rozenberg

doi:10.1016/S0019-9958(79)90082-2

Equality languages and fixed point languages

Joost Engelfriet, Grzegorz Rozenberg

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Abstract

This paper considers equality languages and fixed-point languages of homomorphisms and deterministic gsm mappings. It provides some basic properties of these classes of languages. We introduce a new subclass of dgsm mappings, the so-called symmetric dgsm mappings. We prove that (unlike for arbitrary dgsm mappings) their fixed-point languages are regular but not effectively obtainable. This result has various consequences. In particular we strengthen a result from Ehrenfeucht, A., and Rozenberg, G. [(1978), Theor. Comp. Sci. 7, 169–184] by pointing out a class of homomorphisms which includes elementary homomorphisms but still has regular equality languages. Also we show that the result from Herman, G. T., and Walker, A. [(1976), Theor. Comp. Sci. 2, 115–130] that fixed-point languages of DIL mappings are regular, is not effective.

Original language	English
Pages (from-to)	20-49
Journal	Information and Control
Volume	43
Issue number	1
DOIs	https://doi.org/10.1016/S0019-9958(79)90082-2
Publication status	Published - 1979
Externally published	Yes

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AB - This paper considers equality languages and fixed-point languages of homomorphisms and deterministic gsm mappings. It provides some basic properties of these classes of languages. We introduce a new subclass of dgsm mappings, the so-called symmetric dgsm mappings. We prove that (unlike for arbitrary dgsm mappings) their fixed-point languages are regular but not effectively obtainable. This result has various consequences. In particular we strengthen a result from Ehrenfeucht, A., and Rozenberg, G. [(1978), Theor. Comp. Sci. 7, 169–184] by pointing out a class of homomorphisms which includes elementary homomorphisms but still has regular equality languages. Also we show that the result from Herman, G. T., and Walker, A. [(1976), Theor. Comp. Sci. 2, 115–130] that fixed-point languages of DIL mappings are regular, is not effective.

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VL - 43

SP - 20

EP - 49

JO - Information and Control

JF - Information and Control

IS - 1

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Equality languages and fixed point languages

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