Returns all successors to the specific node.

        :param node: A node in the graph.
        :return:     A set of nodes that are all successors to the given node.
        :rtype:      set

def all_successors(self, node, skip_reached_fixedpoint=False):
        """
        Returns all successors to the specific node.

        :param node: A node in the graph.
        :return:     A set of nodes that are all successors to the given node.
        :rtype:      set
        """

        successors = set()

        stack = [ node ]
        while stack:
            n = stack.pop()
            successors.add(n)
            stack.extend(succ for succ in self.successors(n) if
                         succ not in successors and
                            (not skip_reached_fixedpoint or succ not in self._reached_fixedpoint)
                         )

        return successors