Undecidability of infinite post correspondence problem for instances of size 8
RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications, Tome 46 (2012) no. 3, pp. 451-457.

The infinite Post Correspondence Problem (ωPCP) was shown to be undecidable by Ruohonen (1985) in general. Blondel and Canterini [Theory Comput. Syst. 36 (2003) 231-245] showed that ωPCP is undecidable for domain alphabets of size 105, Halava and Harju [RAIRO-Theor. Inf. Appl. 40 (2006) 551-557] showed that ωPCP is undecidable for domain alphabets of size 9. By designing a special coding, we delete a letter from Halava and Harju's construction. So we prove that ωPCP is undecidable for domain alphabets of size 8.

DOI : 10.1051/ita/2012015
Classification : 03D35, 03D40, 68R15
Mots-clés : ωPCP, semi-Thue system, undecidable, theory of computation 
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     title = {Undecidability of infinite post correspondence problem for instances of size 8},
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Dong, Jing; Liu, Qinghui. Undecidability of infinite post correspondence problem for instances of size 8. RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications, Tome 46 (2012) no. 3, pp. 451-457. doi : 10.1051/ita/2012015. http://www.numdam.org/articles/10.1051/ita/2012015/

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