Circuit Satisfiability and Constraint Satisfaction Around Skolem Arithmetic
We study interactions between Skolem Arithmetic and certain classes of Circuit Satisfiability and Constraint Satisfaction Problems (CSPs). We revisit results of Glaser et al. [16] in the context of CSPs and settle the major open question from that paper, finding a certain satisfiability problem on circuits—involving complement, intersection, union and multiplication—to be decidable. This we prove using the decidability of Skolem Arithmetic. Then we solve a second question left open in [16] by proving a tight upper bound for the similar circuit satisfiability problem involving just intersection, union and multiplication. We continue by studying first-order expansions of Skolem Arithmetic without constants, \((\mathbb {N};\times )\), as CSPs. We find already here a rich landscape of problems with non-trivial instances that are in P as well as those that are NP-complete.