 Conditional Entailment is another assumption-based approach  (Geffner and Pearl 1992).  Suppose we start with a theory \(T = (\Delta, \Gamma, \Lambda)\) where \(\Delta = \{\phi_i \rightarrow \psi_i \mid i \in I\}\) consists of default rules, \(\Gamma\) consists of necessary facts, while \(\Lambda\) consists of contingent facts. It is translated into an assumption-based theory \(T' = (\Delta', \Gamma', \Lambda)\) as follows: 