def __init__(self, graphs, store="default"):
        if store is not None:
            super(ReadOnlyGraphAggregate, self).__init__(store)
            Graph.__init__(self, store)
            self.__namespace_manager = None

        assert (
            isinstance(graphs, list)
            and graphs
            and [g for g in graphs if isinstance(g, Graph)]
        ), "graphs argument must be a list of Graphs!!"
        self.graphs = graphs