@Override
public V getEdgeTarget(E edge) {
return containsEdge(edge) ? graph.getEdgeTarget(edge) : null;
}
@Override
public boolean containsEdge(E edge) {
return (vertices.contains(graph.getEdgeSource(edge))
&& vertices.contains(graph.getEdgeTarget(edge))
&& graph.containsEdge(edge));
}
