Return a sorted list of strings representing all possible actions
        of the form: nonterminal -> [right_hand_side]

def all_possible_actions(self) -> List[str]:
        """
        Return a sorted list of strings representing all possible actions
        of the form: nonterminal -> [right_hand_side]
        """
        all_actions = set()
        for _, action_list in self.valid_actions.items():
            for action in action_list:
                all_actions.add(action)
        return sorted(all_actions)