 Zellner points out that, since Tom would \(\langle{\sim}B\rangle\) if he were to \(\langle A\rangle\), the value of performing \(\langle A\rangle\) is not uniquely optimific even though the value of performing \(\langle A \lamp B\rangle\) is uniquely optimific. Thus, in such cases,  (U)  combined with  (ODC)  still generates contradictions, even if each act is indexed to their respective times. Zellner argued that, to solve the problem, (U) should be rejected because it is inconsistent with a supposedly basic principle of inference, referred to as (NI), which holds that if an agent is obligated to perform \(\langle A\rangle\) and her performing \(\langle A\rangle\) entails her performing \(\langle B\rangle\), then she is obligated to perform \(\langle B\rangle\) (1972: 125). This rule is sometimes referred to as Normative Inheritance or as Permissibility is Closed Under Implication. It may be represented more formally in the Standard Deontic Logic system as (Feldman 1986: 41):