 Dag Prawitz (1970) and Fred Westphal (1972) both suggested revising  (U)  by indexing actions to the time they would need to be performed in order to bring about the uniquely optimific outcome. So, if performing the joint act \(\langle A \at t_1 \lamp B \at t_2\rangle\) would result in the greatest net amount of good, then S is obligated to perform \(\langle A \at t_1\rangle\) and to perform \(\langle B \at t_2\rangle\) and, Westphal claims, this avoids the contradiction. At \(t_1\), \(\langle A\rangle\) supposedly is the act that would produce the greatest net amount of good in comparison to any other act performable at \(t_1\). At \(t_2\), \(\langle B\rangle\) supposedly is the act that would produce the greatest net amount of good in comparison to any other act performable at \(t_2\). Finally, from among the performable act-sets that might occur from \(t_1\)–\(t_2\), \(\langle A \lamp B\rangle\) is the act-set that would produce the greatest net amount of good. Thus, each act is the uniquely optimific act at the time it is performed, or so Westphal claims. Notably, Prawitz (1968, 1970) and Westphal (1972) each argue that an act is permissible if and only if it is part of an act-set that, if performed, would bring about the greatest net good of any of the acts available to the agent. In making this argument, Prawitz and Westphal were giving what may be considered the earliest defenses of possibilism. However, they did not yet refer to this view as possibilism. 