Acta Informatica

, Volume 19, Issue 4, pp 357-367

First online:

On some variants of Post's Correspondence Problem

  • Keijo RuohonenAffiliated withInstitute of Mathematics, Tampere University of Technology

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A variant of Post's Correspondence Problem is considered where two different index words are allowed provided that one of them can be obtained from the other by permuting a fixed number of subwords. It is shown that this variant is undecidable. Post's Correspondence Problem is also extended to circular words, doubly infinite words and doubly infinite powers of words, and shown to be undecidable in all these extensions.