Taming Past LTL and Flat Counter Systems
Arnaud Sangnier, University Paris Diderot-Paris 7, France
Date and Time
Tuesday, April 24th, 2012 at 10:30
Polacksbacken, room 1113
Reachability and LTL model-checking problems for flat counter systems are known to be decidable but whereas the reachability problem can be shown in NP, the best known complexity upper bound for the latter problem is made of a tower of several exponentials. Herein, we show that the problem is only NP-complete even if LTL admits past-time operators and arithmetical constraints on counters. Actually, the NP upper bound is shown by adequately combining a new stuttering theorem for Past LTL and the property of small integer solutions for quantifier-free Presburger formulae. Other complexity results are proved, for instance for restricted classes of flat counter systems.
This is a joint work with Stéphane Demri (LSV) and Amit Kumar Dhar (LIAFA)