RAIRO-Theor. Inf. Appl.
Volume 46, Number 3, July-September 2012
|Page(s)||451 - 457|
|Published online||22 June 2012|
Undecidability of infinite post correspondence problem for instances of size 8
Received: 11 November 2011
Accepted: 9 May 2012
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.
Mathematics Subject Classification: 03D35 / 03D40 / 68R15
Key words: ωPCP / semi-Thue system / undecidable / theory of computation
© EDP Sciences 2012
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