Publication at Faculty of Mathematics and Physics |
2023
Abstract
We prove that QCSP(ℕ; x = y RIGHTWARDS ARROW y = z) is PSpace-complete, settling a question open for more than ten years. This completes the complexity classification for the QCSP over equality languages as a trichotomy between Logspace, NP-complete and PSpace-complete.
We additionally settle the classification for bounded alternation QCSP(Γ), for Γ an equality language. Such problems are either in Logspace, NP-complete, co-NP-complete or rise in complexity in the Polynomial Hierarchy.