+ /**
+ * @brief Determines the event in the configuration whose associated
+ * transition is the latest of the given actor
+ *
+ * @invariant: At most one event in the configuration will correspond
+ * to `preEvt(C, a)` for any action `a`. This can be argued by contradiction.
+ *
+ * If there were more than one event (`e` and `e'`) in any configuration whose
+ * associated transitions `a` were run by the same actor at the same step, then they
+ * could not be causally related (`<`) since `a` could not be enabled in
+ * both subconfigurations C' and C'' containing the hypothetical events
+ * `e` and `e` + `e'`. Since they would not be contained in each other's histories,
+ * they would be in conflict, which cannot happen between any pair of events
+ * in a configuration. Thus `e` and `e'` cannot exist simultaneously
+ */
+ std::optional<const UnfoldingEvent*> get_latest_event_of(aid_t) const;
+ /**
+ * @brief Determines the most recent transition of the given actor
+ * in this configuration, or `pre(a)` as denoted in the thesis of
+ * The Anh Pham
+ *
+ * Conceptually, the execution of an interleaving of the transitions
+ * (i.e. a topological ordering) of a configuration yields a unique
+ * state `state(C)`. Since actions taken by the same actor are always
+ * dependent with one another, any such interleaving always yields a
+ * unique
+ *
+ * @returns the most recent transition of the given actor
+ * in this configuration, or `std::nullopt` if there are no transitions
+ * in this configuration run by the given actor
+ */
+ std::optional<const Transition*> get_latest_action_of(aid_t aid) const;
+ std::optional<const UnfoldingEvent*> pre_event(aid_t aid) const { return get_latest_event_of(aid); }
+