Compiling Finite Domain Constraints to SAT with BEE: the Director's Cut

BEE is a compiler which facilitates solving finite domain constraints by encoding them to CNF and applying an underlying SAT solver. In BEE constraints are modeled as Boolean functions which propagate information about equalities between Boolean literals. This information is then applied to simplify the CNF encoding of the constraints. We term this process equi-propagation. A key factor is that considering only a small fragment of a constraint model at one time enables to apply stronger, and even complete reasoning to detect equivalent literals in that fragment. Once detected, equivalences propagate to simplify the entire constraint model and facilitate further reasoning on other fragments. BEE is described in several recent papers: [20], [19] and [21]. In this paper, after a quick review of BEE, we elaborate on two undocumented details of the implementation: the hybrid encoding of cardinality constraints and complete equi-propagation. We then describe ongoing work aimed to extend BEE to consider binary representation of numbers.