Multi-buffer simulations: Decidability and complexity

Overview & Synopsis

Multi-buffer simulation is a refinement of fair simulation between two nonde-terministic B ¨ uchi automata (NBA). It is characterised by a game in which letters get pushed to and taken from FIFO buffers of bounded or unbounded capacity. Games with a single buffer approximate the PSPACE-complete language inclusion problem for NBA. With multiple buffers and a fixed mapping of letters to buffers these games approximate the undecidable inclusion problem between Mazurkiewicz trace languages. We study the decidability and complexity of multi-buffer simulations and obtain the following results: P-completeness for fixed bounded buffers, EXPTIME-completeness in case of a single unbounded buffer and high undecidability (in the analytic hierarchy) with two buffers of which at least one is unbounded. We also consider a variant in which the buffers are kept untouched or flushed and show PSPACE-completeness for the single-buffer case.