Note: A shorter proof that palindromes are not a Church-Rosser language, with extensions to almost-confluent and preperfect Thue systems

Authors:
Colm ÓDúnlaing;Natalie Schluter
Affiliations:
Mathematics,11Mathematics department website: http://www.maths.tcd.ie. Trinity College, Dublin 2, Ireland;Mathematics,11Mathematics department website: http://www.maths.tcd.ie. Trinity College, Dublin 2, Ireland
Venue:
Theoretical Computer Science
Year:
2010

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Abstract

In 2002, Jurdzinski and Lorys settled a long-standing conjecture that palindromes are not a Church-Rosser language. Their proof involved a difficult analysis of computation graphs associated with 2-pushdown-stack automata. We present a shorter and easier proof in terms of 1-tape Turing machines. We also discuss how the proof generalises to almost-confluent Thue systems and the differing powers of Church-Rosser, almost-confluent, and preperfect Thue systems in relation to palindromes.