A Survey of Satisfiability Modulo Theory <s> Natural-Domain SMT <s> The DPLL approach to the Boolean satisfiability problem (SAT) is a combination of search for a satisfying assignment and logical deduction, in which each process guides the other. We show that this approach can be generalized to a richer class of theories. In particular, we present an alternative to lazy SMT solvers, in which DPLL is used only to find propositionally satisfying assignments, whose feasibility is checked by a separate theory solver. Here, DPLL is applied directly to the theory. We search in the space of theory structures (for example, numerical assignments) rather than propositional assignments. This makes it possible to use conflict in model search to guide deduction in the theory, much in the way that it guides propositional resolution in DPLL. Some experiments using linear rational arithmetic demonstrate the potential advantages of the approach. <s> BIB001 </s> A Survey of Satisfiability Modulo Theory <s> Natural-Domain SMT <s> SMT solvers have traditionally been based on the DPLL(T) algorithm, where the driving force behind the procedure is a DPLL search over truth valuations. This traditional framework allows for a degree of modularity in the treatment of theory solvers. Over time, theory solvers have become more and more closely integrated into the DPLL process, and consequently less and less modular. In this paper, we present a DPLL-like algorithm for SMT solving in which the search takes place over the natural domain of the variables in the problem. As a case study, we analyze its application to continuous domain linear arithmetic, present implementation techniques and some experimentation with difference logic. Results indicate the method can sometimes outperform leading SMT solvers but that the method is not yet robust. <s> BIB002
In DPLL(T) there is a fundamental difference between propositional and other kinds of unknowns: the second are never dealt with directly during the search process. In contrast, in natural-domain SMT, one directly constrains and assigns to numeric unknowns during the search. After initial attempts BIB002 BIB001 , two main directions arose.