Fixed-Parameter Tractability of Disjunction-FreeDefault Reasoning

In this paper, the parameter which is the source of the complexity of disjunction-free default reasoning is determined. It is shown that when the value of this parameter is xed, the disjunction-free default reasoning can be solved in time bounded by a polynomial whose degree does not depend on the parameter. Consequently, disjunction-free default reasoning is xed parameter tractable.