a domain theory is "perfect" or "complete" if it contains, in principle, all information needed to decide any question about the domain. for example, the domain theory for chess is simply the rules of chess. knowing the rules, in principle, it is possible to deduce the best move in any situation. however, actually making such a deduction is impossible in practice due to combinatoric explosion. ebl uses training examples to make searching for deductive consequences of a domain theory efficient in practice.