Relative Undecidability in Term Rewriting Part 2: The Confluence Hierarchy

For a hierarchy of properties of term rewriting systems related to confluence we prove relative undecidability, i.e., for implications X ⇒ Y in the hierarchy the property X is undecidable for term rewriting systems satisfying Y . For some of the implications either X or ¬X is semi-decidable, for others neither X nor ¬X is semi-decidable. We prove most of these results for linear term rewrite systems.