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Systems of equations over a free monoid and Ehrenfeucht’s conjecture. (English) Zbl 0528.68057

##### MSC:
 68Q45 Formal languages and automata 20M05 Free semigroups, generators and relations, word problems 20M35 Semigroups in automata theory, linguistics, etc. 68Q42 Grammars and rewriting systems
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##### References:
 [1] J. Albert, K. Culik II and J. Karhumaki, Test sets for context free languages and systems of equations over a free monoid, Inform. and Control, to appear. · Zbl 0477.68082 [2] Berstel, J., Transductions and context free languages, (1979), B.G. Teubner Stuttgart · Zbl 0424.68040 [3] Culik, K., Homomorphisms: decidability, equality and test sets, () [4] Culik, K.; Fris, I., The decidability of the equivalence problem for DOL systems, Inform. and control, 35, 20-39, (1977) · Zbl 0365.68074 [5] Culik, K.; Karhumaki, J., On the equality sets for homomorphisms on free monoids with two generators, R.A.I.R.O. theoretical informatics, 14, 349-369, (1980) · Zbl 0454.20048 [6] Culik, K.; Salomaa, A., On the decidability of homomorphism equivalence for languages, Jcss, 17, 163-175, (1978) · Zbl 0389.68042 [7] Culik, K.; Salomaa, A., Test sets and checking words for homorphism equivalence, Jcss, 379-395, (1980) · Zbl 0451.68046 [8] Ehrenfeucht, A.; Rozenberg, G., Simplication of homomorphisms, Inform. and control, 38, 289-309, (1978) · Zbl 0387.68062 [9] Harrison, M.A., Introduction to formal language theory, (1978), Addison-Wesley Reading, MA · Zbl 0411.68058 [10] Karhumaki, J.; Simon, I., A note on elementary homomorphisms and the regularity of equality sets, EATCS bulletin, 9, 16-24, (1979) [11] M. Karpinski, ed., New Scottish Book of Problems, in preparation. [12] Linna, M., The decidability of the DOL prefix problem, Internat. J. of computer mathematics, 6, 127-142, (1977) · Zbl 0358.68114 [13] Makanin, G.S., The problem of solvability of equations in a free semigroup (in Russian), Matematiceskij sbornik, 103, 145, 148-236, (1977) · Zbl 0371.20047 [14] Rozenberg, G.; Salomaa, A., The mathematical theory of L systems, (1980), Academic Press New York · Zbl 0365.68072
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