ASSAT (Answer Sets by SAT solvers) is a system for computing answer sets of a logic program by using SAT solvers. Briefly speaking, given a ground logic program P, ASSAT(X), depending on the SAT solver X used, works as follows: Computes the completion of P and converts it into a set C of clauses. Repeats Calls X on C to get a model M (terminates with failure if no such M exists). If M is an answer set of P, then returns with it. Otherwise, finds some loops in P whose loop formulas are not satisfied by M and adds their corresponding clauses to C.