UndirectedEdgeContainer(EdgeSetFactory<VV, EE> edgeSetFactory, VV vertex) {
   vertexEdges = edgeSetFactory.createEdgeSet(vertex);
 }
 DirectedEdgeContainer(EdgeSetFactory<VV, EE> edgeSetFactory, VV vertex) {
   incoming = edgeSetFactory.createEdgeSet(vertex);
   outgoing = edgeSetFactory.createEdgeSet(vertex);
 }