Return the subgraph of this graph whose vertices
        are the given ones and whose edges are the edges
        of the original graph between those vertices.

def full_subgraph(self, objects):
        """
        Return the subgraph of this graph whose vertices
        are the given ones and whose edges are the edges
        of the original graph between those vertices.

        """
        vertices = ElementTransformSet(transform=id)
        out_edges = KeyTransformDict(transform=id)
        in_edges = KeyTransformDict(transform=id)
        for obj in objects:
            vertices.add(obj)
            out_edges[obj] = []
            in_edges[obj] = []

        edges = set()
        head = {}
        tail = {}

        for referrer in vertices:
            for edge in self._out_edges[referrer]:
                referent = self._head[edge]
                if referent not in vertices:
                    continue
                edges.add(edge)
                tail[edge] = referrer
                head[edge] = referent
                out_edges[referrer].append(edge)
                in_edges[referent].append(edge)

        return ObjectGraph._raw(
            vertices=vertices,
            edges=edges,
            out_edges=out_edges,
            in_edges=in_edges,
            head=head,
            tail=tail,
        )