+ * state, viz. those that are enabled for this actor
+ *
+ * Most actors can take only a single action from any given state.
+ * However, when an actor executes a transition with multiple
+ * possible variations (e.g. an MC_Random() [see class: RandomTransition]
+ * for more details]), multiple enabled actions are defined
+ *
+ * @invariant The transitions are arranged such that an actor
+ * with multiple possible paths of execution will contain all
+ * such transitions such that `pending_transitions_[i]` represents
+ * the variation of the transition with `times_considered = i`.
+ *
+ * TODO: If only a subset of transitions of an actor that can
+ * take multiple transitions in some state are truly enabled,
+ * we would instead need to map `times_considered` to a transition,
+ * as the map is currently implicit in the ordering of the transitions
+ * in the vector