21. A constraint satisfaction problem may be relationally consistent, have no empty domain or unsatisfiable constraint, and yet be unsatisfiable . 22. This addition makes the constraint store unsatisfiable , and the interpreter backtracks, removing the last addition from the constraint store. 23. A " minimum unsatisfiable core " contains the smallest number of the original clauses required to still be unsatisfiable. 24. A " minimum unsatisfiable core " contains the smallest number of the original clauses required to still be unsatisfiable . 25. To show that a formula A is provable, the tableaux method attempts to demonstrate that the negation of A is unsatisfiable . 26. One of these conjunctions may contain a pair of complementary literals, in which case that conjunction is proved to be unsatisfiable . 27. On the other hand, it seems to be very difficult to determine the value of an unsatisfiable game, even approximately. 28. With this variant, a proof for an unsatisfiable set can always be found by a suitable policy of application of the other rules. 29. This is because the only way such calculi cannot generate a closed tableau from an unsatisfiable set is by not applying some applicable rules. 30. In spite of this reduction of choices, the completeness theorem implies that a closed tableau can be found if the set is unsatisfiable .
