def get_forward_star(self, node):
        """Given a node, get a copy of that node's forward star.

        :param node: node to retrieve the forward-star of.
        :returns: set -- set of hyperedge_ids for the hyperedges
                        in the node's forward star.
        :raises: ValueError -- No such node exists.

        """
        if node not in self._node_attributes:
            raise ValueError("No such node exists.")
        return self._forward_star[node].copy()
Given a node, get a copy of that node's forward star.

        :param node: node to retrieve the forward-star of.
        :returns: set -- set of hyperedge_ids for the hyperedges
                        in the node's forward star.
        :raises: ValueError -- No such node exists.