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

In 2002, Jurdziński and Loryś 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.