The Path-bifurcation Hierarchy Does Not Collapse to \(\Sigma ^1\) in Infinite Abelian Groups
摘要
Some general transfer principles for unit cost complexity problems are proved. As an application, we show that for infinite abelian groups \(\Sigma ^2 \cap \Pi ^2 \neq \Sigma ^1 \cup \Pi ^1\) . This has been shown for the group of real numbers by Herve Fournier and Pascal Koiran using the problem Twenty Questions. As this problem is not appropriate for infinite abelian groups in general, it was replaced here by Null-sack.